(1)(8)f-flt petct as an imaging tool for early prediction of pathological response in patients with...
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7/24/2019 (1)(8)F-FLT PETCT as an Imaging Tool for Early Prediction of Pathological Response in Patients With Locally Advanc
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ORIGINAL ARTICLE
18F-FLT PET/CT as an imaging tool for early prediction
of pathological response in patients with locally advanced breast
cancer treated with neoadjuvant chemotherapy: a pilot study
Flavio Crippa &Roberto Agresti &Marco Sandri &Gabriella Mariani &
Barbara Padovano &Alessandra Alessi &Giulia Bianchi &Emilio Bombardieri &
Ilaria Maugeri &Mario Rampa &Maria Luisa Carcangiu &Giovanna Trecate &
Claudio Pascali &Anna Bogni &Gabriele Martelli &Filippo de Braud
Received: 4 September 2014 /Accepted: 14 January 2015 / Published online: 12 February 2015# Springer-Verlag Berlin Heidelberg 2015
Abstract
P u r p o s e W e e v a l u a t e d w h e t h e r 18F -3 -d eo x y -3 -
fluorothymidine positron emission tomography (FLT PET)
can predict the final postoperative histopathological response
in primary breast cancer after the first cycle of neoadjuvant
chemotherapy (NCT).
MethodsIn this prospective cohort study of 15 patients with
locally advanced operable breast cancer, FLT PET evaluations
were performed before NCT, after the first cycle of NCT, and
at the end of NCT. All patients subsequently underwent sur-
gery. Variables from FLT PET examinations were correlated
with postoperative histopathological results.
ResultsAt baseline, median of maximum standardized up-
take values (SUVmax) in the groups showing a complete
pathological respons e (pCR) + residual cancer burden
(RCB) I, RCB II or RCB III did not differ significantly
for the primary tumour (5.0 vs. 2.9 vs. 8.9, p =0.293) or
for axillary nodes (7.9 vs. 1.6 vs. 7.0, p =0.363), whereas
the Spearman correlation between SUVmax and Ki67 pro-
liferation rate index was significant (r=0.69, p
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Introduction
Neoadjuvant chemotherapy (NCT) followed by surgery is a
standard therapeutic strategy for operable, locally advanced
breast cancer. Several clinical trials have demonstrated good
results, with an objective response rate of about 70 % and a
complete pathological response rate of up to 30 % [14].
These findings have led to improved surgical planning, anincreased rate of breast-conserving surgery even in patients
with an unfavourable tumour/breast size ratio before therapy,
and have enabled further evaluation of the biology of the
response of the primary tumour to chemotherapy and of the
efficacy of chemotherapy [5,6]. It is well known that the type
of pathological response after NCT is a fundamental prognos-
tic factor [512]. However, to date, the efficacy of NCT is
evaluated only upon final histology of the postsurgical speci-
men. Clinical examination and instrumental diagnostic tools,
such as mammography or ultrasound examination, based on
size and morphological criteria fail to predict early a complete
pathological response (pCR) to NCT and later to efficientlydistinguish responders from nonresponders [13]. Thus, there
is a need for a reliable method to assess the early response to
NCT in order to avoid ineffective and expensive therapy and
to provide alternative management options for consideration.
The use of MRI to search for new surrogate markers of
disease response has yielded interesting results in several stud-
ies that have evaluated the functional response to NCT in
breast cancer [14,15]. Some of these studies investigated the
utility of MRI in monitoring response to treatment by using
combined parameters such as diffusion-weighted MRI (DW-
MRI), dynamic contrast enhancement (DCE-MRI), volumet-
rics, and spectroscopy [1619].
PET using different tracers is playing an increasing role in
predicting the response of breast cancer to NCT [20]. At pres-
ent, 18F-fluorodeoxyglucose (FDG) PET is the most common-
ly used method for monitoring response of breast cancer to
treatment, according to published results [2129].
In the present study, we used 18F-fluorothymidine (FLT), a
tracer of proliferation [3032] tested in other pilot studies of
breast cancer [3236], to assess the value of FLT PET in the
early prediction of response of locally advanced operable
breast cancer to NCT and to identify its potential predictive
value based on relative changes in standardized uptake values
(SUV) of FLT PET in primary tumours and axillary nodes
after the first cycle of NCT.
Patients and methods
Patient population and treatment
This prospective cohort pilot study comprised patients with
potentially operable, locally advanced T2-3 breast cancer
treated with NCT followed by surgery at our institute.
Pretreatment histological diagnosis of invasive breast carcino-
ma was done by core needle biopsy in all patients and further
characterized for hormone receptor status, HER2 status and
prolif erativ e in dex. In it ial routine staging proced ures
consisted of clinical examination and mammographic and ul-
trasound evaluation of tumour size and axillary nodal status.
Chest plain radiography, whole-body bone scan and ultra-sound examination of the liver and abdomen were used to
assess distant metastases.
NCT consisted of an anthracycline/taxane-based regimen
for six cycles, with trastuzumab administered to those with
HER2-positive breast cancer. Specifically, the NCT regimen
included doxorubicin (60 mg/m2) + paclitaxel (200 mg/m2)
every 3 weeks for three cycles followed by cyclophospha-
mide/methotrexate/fluorouracil (600/40/600 mg//m2) on days
1 and 8 every 4 weeks for three cycles, and trastuzumab in
patients with HER2-positive breast cancer (8 mg/kg loading
dose decreased to 6 mg/kg) every 4 weeks for three cycles
concomitant with cyclophosphamide/methotrexate/fluorouracil.
Patients underwent breast-conserving surgery or total mas-
tectomy according to the clinical and instrumental response to
NCT, site of tumour inside the breast, cosmetic evaluation,
pr es en ce of ex te ns iv e in tr ad uc ta l co mp on en t an d/ or
multifocality. Axillary surgery (complete dissection or senti-
nel node biopsy) was performed based on clinical nodal status
before and after NCT. Nuclear medicine physicians, surgeons
and pathologists performed their work blinded to other results.
The institutional review board or equivalent approved this
study, and all subjects signed written informed consent.
PET evaluation
18F-3-Deoxy-3-fluorothymidine (FLT) was synthesized and
prepared by the Radiochemistry and Cyclotron Facility of our
Institute as previously described [37]. To minimize potential
pitfalls due to FLT metabolism, patients fasted for at least 6 h
before receiving approximately 3.5 MBq/kg of FLT adminis-
tered intravenously as a bolus, followed by 10 ml of normal
saline (0.9 % NaCl). Images were obtained 80 min after injec-
tion of FLT, in accordance with the work of Smyczek-Gargya
et al. [38] and with our previous unpublished studies on dif-
ferent tumours. A hybrid PET/CT system (64 TOF Gemini;
Philips Medical Systems) was used in the present study.
During the waiting period, patients were asked to drink 0.5 l
of water to reduce bladder activity and radiation exposure to
the bladder and to use the bathroom 30 min after FLT admin-
istration and immediately before the start of the PET study.
The imaging protocol included a CT scout scan to define the
axial imaging range (from upper thigh to skull base), a low-
dose CT scan without contrast enhancement, and lastly, a
three-dimensional PET scan (3 min per bed position). CT
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images, obtained with the patient breathing shallowly,
were used for attenuation correction of the PET data
and anatomical positioning of the FLT findings. Each
patient was studied before therapy (time-point t0), after
one cycle of chemotherapy (time-point t1) and after
completion of therapy (time-point t2), about 1 month
before surgery. Figure 1 shows the flow chart of the
study with the three FLT PET evaluations.Using dedicated PET workstations (Philip Extended
Brilliance Workspace), nuclear medicine physicians
blinded to each patients history and clinical and con-
ventional imaging findings visually analysed the PET/
CT images, looking especially for areas of focally in-
creased FLT uptake in the breast tumour and ipsilateral
axillary regions. FLT uptake was evaluated semiquanti-
tatively using the SUVmax defined as the highest SUV
in a region of interest and calculated as: SUV= (tissue
activity in megabecquerels per gram)/(injected activity
in megabecquerels)/(body weight in grams). SUVmax
was measured in the primary breast tumour (SUVTmax)and, when detectable, in the dominant axillary lymph
node (SUVNmax) lesions, the latter defined as the largest
lymph node and the highest FLT uptake among the de-
tectable nodes in the fused PET/CT images. During the
course of NCT, changes in SUVmax in target lesions
were monitored by comparing FLT uptake at time points
t0, t1 and t2, and the results are expressed as absolute
value and relative percentage change in SUVmax:
SUVmax ti 100 SUVmax ti SUVmax t0 .
SUVmax t0
wherei is 1 or 2.
Pathological examination and evaluation criteria
To assess pathological response, we opted for the web-based
MD Anderson Residual Cancer Burden (RCB) calculator
[39]. This method, proposed by Symmans et al. [8], allows
c a l c u l a t i o n o f a n i n d e x t h a t c o m b i n e s p a t h o l o g y
measurements of the primary tumour (size and cellularity)
and nodal metastases (number and size):
RCB index1:4 finvdprim 0:17 4 10:75LN dmet
0:17
where finv is the proportion of the primary tumour bed that
contains invasive carcinoma, LN is the number of axillary
lymph nodes containing metastatic carcinoma, dmetis the di-ameter of the largest metastasis in an axillary lymph node, and
dprimffiffiffiffiffiffiffiffiffiffid1d2
p whered1andd2are the bidimensional diame-
ters of the primary tumour bed in the resection specimen [8].
Using two cut-off points, the authors proposed four RCB
categories (RCB 0, RCB I, RCB II and RCB III) correspond-
ing to pCR, minimal residual disease (near-complete re-
sponse), moderate residual disease, and extensive residual dis-
ease, respectively (Table1).
In addition, based on our previous experience, we chose a
cut-off level of 3 for the RCB index, since this value,
contained in the RCB II class (moderate response), may rep-
resent the threshold separating patients with RCB II into those
who show a partial response and are closer to RCB I patients
and those with a partly nonresponding large tumour in pro-
gression. Hence, this cut-off allowed the study population to
be split into two groups: complete/partial responders and
complete/partial nonresponders.
All pathological assessments and immunohistochemistry
were performed at the Pathology Unit of our institute.
Surgical specimens were fixed in neutral formalin and embed-
ded in paraffin, and sections were stained with haematoxylin
and eosin at 4 C. Tumour grade was assessed according to the
procedure of Elston and Ellis [40]. Immunohistochemistry for
oestrogen receptor (ER), progesterone receptor (PgR) and hu-
man epidermal growth factor receptor 2 (HER2) was per-
formed on 4-m-thick sections of breast cancer resection
specimens, whereas immunostaining for Ki67 was performed
on both breast cancer resection specimens and metastatic
axillary lymph nodes. Staining for ER (clone SP1,
Ventana), PgR (clone SP2, Ventana), HER2 (p185,
Dako, diluted 1:1,000), Ki67 (MIB1, Dako, diluted
Fig. 1 Flow chart of the study. The neoadjuvant chemotherapy (NCT)regimen comprised doxorubicin + paclitaxel for three cycles (grey
squares) followed by cyclophosphamide/methotrexate/fluorouracil for
three cycles (white squares). SUVmax(t1) and SUVmax(t2) arerelative percentage changes in SUVmax measured at t1 and t2 for theprimary breast tumour and for the dominant axillary lymph node
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1:100) was detected using an OPTIview DAB detection
system on a Ventana Ultra benchmark Autostainer.
Positive staining for ER and PgR was defined as nucle-
ar staining in 1 % of the tumour cells, whereas HER2
was assessed based on the intensity of tumour cell
membrane staining, scored as 0 (negative), 1+ (weak),
2+ (moderate) and 3+ (strong) staining in at least 30 %
of the tumour cells. The Ki67 proliferation index of
each case was evaluated based on the percentage of
Ki67-positive cells among at least 200 tumour cells.Our pathological reports included an explicit statement
concerning assessment for the presence and degree of
response to chemotherapy.
Statistical analysis
The hypothesis thatkindependent samples come from popu-
lations with the same median was tested using the Kruskal-
Wallis nonparametric rank test. Differences were considered
significant atp0.05.
A linear score based on relative percentage change in
maximum SUV att1in the primary tumour and in the domi-
nant axillary node was proposed for predictive purposes:
SUVTmax t1 SUVNmax t1
where the coefficients, and were estimated using a linear
regression model withSUVTmax(t1) andSUVNmax(t1) as
explanatory variables and the RCB index as outcome variable.
The predictive powers ofSUVTmax(t1), SUVNmax(t1)
and of thescore were assessed by estimating the area under
the ROC curve (AUC). The 95 % confidence intervals (CI) for
AUC and the Pvalue of the test of the null hypothesis that
AUC=0.5 (no predictivity) were estimated using bootstrap
methods with 1,000 replications. Overall accuracy, sensitivity,
specificity, and positive and negative predictive values (PPV
and NPV, respectively) were also estimated for some cut-off
values of the two parameters.
Statistical analyses were performed using Stata13
(StataCorp, College Station, TX) and R (version 3.1.2; R
Foundation for Statistical Computing, Vienna, Austria)
software.
Results
From October 2011 to January 2013, 15 T2-3 N0-1 patients
were accrued to the present study. The median age was
42 years (range 29 63 years). All patients underwent the
three scheduled scans. Figure2shows an example of the im-
aging of the breast tumour and axillary involved nodes on the
baseline FLT PET scan (time t0; Fig.2a), and the progressiveresponse to NCT on the interim (time t1) and final (time t2)
scans compared with baseline (Fig.2b). All patients tolerated
the PET scanning protocol well and all breast lesions were
visualized by FLT PET.
All but one patient, who exhibited progressive dis-
ease after the first three cycles of the doxorubicin/
pa cl it ax el re gi me n, co mp le te d th e sc hedu le d NC T.
Consistent with protocol indications, five patients with
HER2 amplification received trastuzumab. All patients
underwent breast surgery and axillary surgery. Eight pa-
tients underwent total mastectomy (in two due to
microcalcifications with multicentric foci of intraductaldisease), two underwent nipple-sparing mastectomy
(based on breast size and the site of the tumour in order
to achieve the best cosmetic result), and five underwent
quadrantectomy). Ten patients underwent complete axil-
lary dissection, two sentinel node biopsy followed by
axillary dissection, and three sentinel node biopsy only.
Pathological evaluation of surgical specimens according
to previously described classifications [39] identified six
high responders (RCB 0 or RCB I), five weak re-
sponders (RCB II) and four nonresponders (RCB III).
Table2summarizes the clinical, radiological and path-
ological characteristics of the entire patient cohort and
of the three RCB groups at t0. Furthermore, breast can-
cer subtype in all patients was also classified according
to the consensus of the St Gallen International Expert
Panel members [41]. The baseline characteristics of pri-
mary tumours did not differ significantly among the
RCB groups, except for the Ki67 proliferation index.
The mean postoperative pathological tumour size was
15.5 mm (range 0 40 mm) in the entire patient co-
hort, whereas, consistent with the RCB classification,
tumour size differed greatly between the RCB 0 +
RCB I group (3.5 mm) and the other two RCB groups
(RCB II 23.6 mm, RCB III 23.3 mm), as did the rates
of postoperative histologically negative axillary nodes,
where rates were higher in the RCB 0 + RCB I group
(66.7 %) than in the RBC II group (40.0 %) and the
RCB III group (0.0 %).
Table3summarizes the median FLT PET SUVmaxatt0,t1andt2 and the relative percentage changes att1 and t2 in the
primary tumours and in the axillary nodes in the three RCB
groups. The median time (with range) of the interval between
first chemotherapy and PET at baseline was 15 (1 29) days;
Table 1 RCB categories for classification of residual disease in thebreast and axillary nodes after neoadjuvant chemotherapy
RCB class RCB index Amount of disease
0 0 Pathological complete response
I 0 1.36 Minimal residual disease
II 1.36 3.28 Moderate residual disease
III > 3.28 Extensive residual disease
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the median time of PET t1 after the first cycle of chemotherapy
was 18 days (12 21 days); the median time of PET t2after
the last cycle of chemotherapy (before surgery) was 12 days
(5 27 days).
At baseline, median SUVmax values of the primary
tumours for the RCB 0 + RCB I, RCB II and RCB
III groups were 5.0, 2.6, and 8.4, respectively, and of
the axillary nodes were 7.9, 0.8, and 3.2, respectively
(Table 3). S p earmans c o rr e la t i on a t t0 between
SUVTmax and Ki67 proliferation index was positive,
strong and statistically significant (r=0.69, p
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3. Patients with an RCB index below the threshold level 3(RCB 0+I+partly-responding RCB II) vs. patients with
RCB index >3
The results showed that the two parameters play a
different role in the identification of the RCB response
(Fig. 5). On the one hand, the predictive power of
SUVTmax(t1) was good and statistically significant
for identifying RCB 0 + RCB I responses (AUC 0.91,
95 % CI 0.72 1.00, p52.9% (i.e. a reduction in SUVTmax less
than 52.9 %), SUVNmax(t1) showed excellent accuracy inidentifying subjects with a RCB index above 3 (AUC 1.00,
Table4). In addition, SUVNmax(t1) had an interesting (al-
though not statistically significant) ability to separate subjects
withSUVTmax(t1)>52.9% into two groups: the group of
RCB III patients and a heterogeneous group that included
RCB I and RCB II patients with delayed response to chemo-
therapy, clinically node-negative patients, and those with a
low-proliferating luminal A tumour (AUC 0.77, p=0.119).
The cut-off value SUVNmax(t1)18.0% (i.e. a reduction
in SUVNmaxgreater than or equal to 18.0 %) can be used in
the subgroup with SUVTmax(t1)>52.9% for the identifica-
tion of RCB III patients.Lastly, a predictive score based on SUVTmax(t1) and
SUVNmax(t1) parameters was calculated:
= 0.043SUVTmax(t1)0.013SUVNmax(t1) +
3.060
This score showed good predictive power for all three dis-
crimination problems considered, with AUC 0.94 (pT2 5 (33.3) 3 (50.0) 1 (25.0) 1 (20.0)
Oestrogen receptor,n(%)
Negative 9 (60.0) 5 (83.3) 2 (50.0) 2 (40.0)
Positive 6 (40.0) 1 (16.7) 2 (50.0) 3 (60.0)
HER2,n(%)
Negative 10 (66.7) 2 (33.3) 4 (100.0) 4 (80.0)
Positive 5 (33.3) 4 (66.7) 0 (0.0) 1 (20.0)
Grade,n (%)
2 6 (40.0) 1 (16.7) 2 (50.0) 3 (60.0)
3 9 (60.0) 5 (83.3) 2 (50.0) 2 (40.0)
Nodal involvement (cN),n(%)
Negative 6 (40.0) 4 (66.7) 2 (50.0) 0 (0.0)
Positive 9 (60.0) 2 (33.3) 2 (50.0) 5 (100.0)
Breast cancer subtype, n(%)a
Basal-like 9 (60.0) 5 (83.3) 2 (50.0) 2 (40.0)
Luminal-like 6 (40.0) 1 (16.7) 2 (50.0) 3 (60.0)
aClassified according to the consensus of the St Gallen International Expert Panel members [29]
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Discussion
PET may be a major noninvasive imaging modality for eval-
uating cancer cell proliferation, one of the most important
biological features of malignancies [42]. In this regard, the
most promising PET tracer is currently FLT, a fluorine-
modified thymidine analogue. FLT is phosphorylated by thy-
midine kinase-1 and is not incorporated during DNA synthe-
sis, instead becoming trapped within proliferating cells using
the salvage pathway for DNA synthesis [30,31]. It is widely
accepted that FLT is a marker of cells in the S-phase of the cell
cycle, suggesting its ability to reflect tumour aggressiveness
and response to therapy [30,31,43]. The uptake of FLT has
been linked to cell proliferation rate and has been used to
study proliferation in lymphomas, and breast and lung tu-
mours [4446]. We have also found a significant association
between FLT uptake and Ki67 proliferation index [47] in our
series.
FLT PET has often been compared with FDG PET in the
visualization, diagnosis and staging of several tumour types,
including those of the lung, head and neck, stomach, oesoph-
agus, brain and breast [4853]. In general these clinical studies
demonstrated that tumour uptake of FLT is generally lower
than that of FDG, but it can provide high sensitivity and major
Table 3 SUVmax(median and range) in primary tumours (SUVTmax)and axillary nodes (SUVNmax) after FLT PET scans att0, t1 and t2by RCBgroup, and relative percentage changes in SUVmax(median and range) at
t1 an d t2 in primary tumours (SUVTmax) and axillary nodes(SUVNmax) by RCB group
Predictor Total RCB 0 + RCB I RCB II RCB III pvaluea
SUVTmax
t0 4.0 (1.5 12.1) 5.0 (3.4 10.9) 2.6 (1.5 4.4) 8.4 (2.9 12.1) 0.105
t1 2.6 (1.4 10.5) 2.2 (1.5 4.6) 2.2 (1.4 4.0) 6.2 (1.6 10.5) 0.305t2 0.9 (0.0 9.9) 0.0 (0.0 0.0) 1.3 (0.0 3.4) 5.8 (0.9 9.9) 0.005
SUVTmax
t1 26.2 (80.8 12.9) 55.8 (80.8 11.8) 7.9 (18.8 5.3) 26.2 (44.8 12.9) 0.019
t2 69.0 (100.0 18.2) 100.0 (100.0 100.0) 45.0 (100.0 22.7) 26.2 (69.0 18.2) 0.007
SUVNmax
t0 2.8 (0.0 25.6) 7.9 (1.4 11.2) 0.8 (0.0 2.8) 3.2 (1.0 25.6) 0.128
t1 2.1 (0.0 9.8) 2.7 (1.1 5.7) 0.0 (0.0 3.5) 1.7 (0.0 9.8) 0.201
t2 1.0 (0.0 7.4) 0.7 (0.0 2.3) 0.0 (0.0 2.6) 2.2 (0.0 7.4) 0.285
SUVNmax
t1 46.9 (100.0 25.0) 55.5 (69.5 0.0) 1.0 (100.0 25.0) 46.9 (100.0 18.8) 0.321
t2 69.4 (100.0 37.5) 92.3 (100.0 0.0) 3.1 (100.0 1.0) 69.4 (100.0 37.5) 0.343
aKruskal-Wallis test
Fig. 3 Relative percentagechanges in SUVmaxatt1andt2forthe primary breast tumour[SUVTmax(t1) andSUVTmax(t2)] and the dominantaxillary lymph node[SUVNmax(t1) andSUVNmax(t2)] in each patient,together with their median valuesfor each RCB group. a
SUVTmax(grey lines) andmedianSUVTmax(black lines).bSUVNmax(grey lines) andmedianSUVNmax(black lines)
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specificity because, unlike FDG, it does not accumulate in
areas of inflammatory alteration potentially associated with
cancer therapy, leading to false-positive findings [32, 54].
For staging FLT is of limited value because of its high phys-
iological uptake in the liver and bone marrow and consequentpossible false-negative results in the detection of distant me-
tastases at those sites [32,55].
The potential value of PET in monitoring response to NCT
in breast cancer has been evaluated. However, these studies
were mainly done with FDG PET, with only a few involving
FLT PET in heterogeneous series of patients with different
disease stages, chemotherapeutic regimens and scan
acquisition protocols. In one of these studies, Pio et al. evalu-
ated 14 patients with primary or metastatic breast cancer who
were starting a novel chemotherapy or hormonal therapeutic
regimen, and who underwent sequential FLT PET scans.
Although there were strong clinical and therapeutic differ-ences, FLT PET uptake after the first course of chemotherapy
was significantly correlated with overall response in terms of
late changes in CA27.29 tumour marker levels and tumour
size as measured by CT [33]. In another study in 13 patients
with stage IIIV breast cancer, the response to the 5-fluoro-
uracil/epirubicin/cyclophosphamide (FEC) regimen was eval-
uated by FLT PET performed at baseline and 1 week after the
Fig. 4 Scatter plot of the relativepercentage changes in SUVmaxatt1for the primary breast tumour(SUVTmax) and for thedominant axillary lymph node(SUVNmax) in each patient,with their corresponding RCBgroup and RCB index (inparentheses)
Table 4 Predictive ability ofSUVTmax(t1), SUVNmax(t1) and of the proposed score for three discriminating problems: identification ofpCR +RCB Ipatients, RCB IIIpatients, and patients with RCB index below/above 3
RCB 0+I vs. RCB II+III RCB III vs. RCB 0+I+II RCB index 3
AUC pvaluea AUC pvaluea AUC pvaluea
SUVTmax(t1) 0.91 (0.72 1.00) 52.9 %
0.77 (0.45 1.00) 0.119 1.00
scoreb 0.94 (0.82 1.00)
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first cycle, considering uptake at 90 min and the irreversible
trapping of FLT as the reference parameters. FLT PET was
able to discriminate between clinical response and stable dis-
ease [34]. In a further study the value of FLT PET was inves-
tigated by measuring the early response to docetaxel chemo-
therapy. This study was performed in 20 patients with stage
IIIV breast cancer who were unresponsive to first-line che-
motherapy or progressing on previous therapy, and FLT PET
was performed after the first or the second cycle. Although the
patient population was nonhomogeneous, the PET response
was assessed after two cycles in six patients (compared with
one cycle in the rest), and clinical and instrumental criteria
were used to define response rather than histopathology,
changes in the FLT PET signal were nonetheless predictive
of response to therapy (sensitivity 0.85, specificity 0.80) [35].
More recently, Woolf et al. evaluated 20 patients with locally
advanced breast cancer who underwent FLT PET before and
after the first cycle of a FEC or FEC + docetaxel (FEC-T)
chemotherapy regimen [36]. However, in this series, although
a significant and strong correlation between Ki67 and SUVmaxwas found, neither baseline SUVmaxnorSUVmaxfrom FLT
PET was predictive of response after the first cycle of treat-
ment. Homogeneous SUVmaxreduction in most patients was
the main concern in that study.
At present, there are no definitive indications regarding the
optimal timing of PET after FLT injection [36,38,56]. In our
study, we used static PET imaging acquisitions at 80-min in-
tervals and the semiquantitative SUV method to measure tu-
mour FLT uptake. This is a simple and widely adopted proce-
dure for PET imaging in clinical protocols, providing a sum
total measure of the tumour tracer uptake by metabolic trap-
ping [57]. SUV can be less precise than PET analysis based on
dynamic image acquisitions and kinetic modelling, because it
does not account for the possible contribution of labelled me-
tabolites and perfusion. Nevertheless, in several clinical stud-
ies FLT SUV was significantly correlated with cell prolifera-
tion [5860] and our study aimed to evaluate a method avail-
able in a clinical setting.
This pilot study showed that FLT PET might serve in the
construction of a prediction rule able to discriminate early
between two different populations of patients undergoing
NCT based on the probability of response to the therapy. In
Fig. 5 ROC curves ofSUVTmax(t1) (a,b) and score(c, d;= 0.043SUVTmax(t1)0.013SUVNmax(t1)+3.060)for discriminating pCR+RCB Isubjects (a,c) and not RCB III(i.e. pCR+RCB I and II)subjects (b,d); the main cut-offvalues are plotted on the curves
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particular, a joint analysis of variations in SUVmaxin the pri-
mary tumour and the axillary lymph nodes appears to identify
early mammary tumours will achieve pCR or near pCR (RCB
I) on final histology. The ability to predict early response after
one or two cycles of NCT would avoid unnecessary toxicities
in patients with an unsatisfactory response, with a potential
impact on clinical outcomes and quality of life.
Our results showed that at t1, FLT PET identified threedifferent patient populations: a group with a high rate of re-
sponse both in tumour and axillary nodes; a group with an
initial response at the axillary node level without a similar
final response in the tumour; and a heterogeneous group with
a low rate of response at both levels due to a low-proliferating
luminal A tumour or a clinically node-negative tumour with
delayed response to NCT. Notwithstanding this interesting
ability to identify different populations, SUVTmax(t1) and
SUVNmax(t1) showed substantially different predictive
roles: SUVTmax(t1) seemed able to discriminate between
responders and all other patients, whereasSUVNmax(t1) dis-
criminated between complete nonresponders and moderate/partial responders within the nonresponder group. In addition,
the two parameters may be used to develop a single score with
a significant ability to identify responders, partial responders
and nonresponders.
One crucial issue is the optimal time for performing the
PET scan to evaluate response to NCT. A recent meta-
analysis has shown that the predictive value of FDG PETearly
after therapy (after the first or second cycle of NCT) is signif-
icantly better than after three or more cycles [61], possibly
because PET detects metabolic or proliferative changes in
the tumour before other clinical or radiological tools are able
to detect tumour size shrinkage. In our study, after the baseline
FLT PET att0, we chose to perform the subsequent PET scans
3 weeks after the first cycle of NCT (time t1, immediately
before the second cycle) and at the end of therapy (timet2).
Another crucial point is the definition of a method to eval-
uate the response after NCT. It is well known that the patho-
logical measurement of residual cancer after NCT is an impor-
tant prognostic factor that can influence patient outcome [20].
Recently, a meta-analysis of almost 12,000 patients accrued in
12 international trials has shown that pCR is a valid surrogate
endpoint of long-term clinical benefit, particularly in aggres-
sive tumour subtypes [62]. Consequently, the definition of an
effective method for measuring the percentage of residual dis-
ease [12] and the correct interpretation of the results [63] is
fundamental. In the study NSABP B18, classification was
based on the simple dichotomy between pCR and pINV (his-
tological evidence of less residual invasive carcinoma) [1],
whereas Sataloff et al. [7] graded the response according to
four categories ranging from a total or near-total therapeutic
effect (grade A) to no therapeutic effect (grade D) as assessed
based on microscopic changes such as necrosis, calcifications,
fibrosis and inflammatory infiltration. Ogston et al. [64]
proposed a five-step scale of response based on the progres-
sive reduction in tumour cellularity in the breast only. Finally,
Chollet et al. [65] proposed a new classification based on
residual disease in the breast and nodes (RDBN), which how-
ever is only applicable to patients who have undergone axil-
lary dissection and for discriminating between responders and
nonresponders [66]. As discussed above, we opted for the
web-based MD Anderson RCB calculator [39], which waspreviously defined by Symmans et al. [8] for the evaluation
of response to NCTusing routine pathological features such as
the largest two dimensions (measured in millimetres) of the
tumour bed, percentage of cellularity of the tumour and
intraductal disease, number of nodal metastases, and size of
the largest nodal metastasis. In our opinion, this four-group
RCB classification, that gives an accurate calculated value for
each patient, allowed the best evaluation of response for sta-
tistical analysis.
Until now, response of breast cancer to NCT has usually
been evaluated in clinical studies with FDG PET. One of the
first studies evaluated 47 patients treated with different che-motherapy regimens, and FDG PET predicted pCR with a
sensitivity of 91 % and a specificity of 86 % [21 ].
Interestingly, in multivariate analysis SUV appeared to be
the only predictive factor of pCR. A further study confirmed
the significant value of FDG PET in predicting response to
NCT (sensitivity 77 %, specificity 80 %, AUC 0.82) in 50
patients treated with a more homogeneous chemotherapy reg-
imen, considering the changes in SUVmaxbetween baseline
and after the second cycle of chemotherapy [22].
More recently, several studies have assessed the predictive
value of FDG PET in different molecular subtypes of breast
cancer. Groheux et al. studied the response to NCT in terms of
FDG uptake in patients with stage II/III HER2-positive breast
cancer [23] and triple-negative breast cancer [24]. In the first
group of 30 HER2-positive patients, using a homogeneous
chemotherapy regimen, ROC analysis showed that the best
predictive result in terms of pCR after two cycles of chemo-
therapy was characterized by an AUC of 0.91, with a sensi-
tivity of 86 % and a specificity of 94 %. This highlights the
ability of FDG PET to identify the group of patients without
pCR [23]. Similarly, in a second group of 50 triple-negative
patients, FDG PET was performed before treatment and after
two cycles of chemotherapy, and theSUVmax in the primary
tumour was the most effective parameter for predicting pCR
(AUC 0.84) [24].
Koolen et al. have also found that FDG PET is of value in
predicting pathology outcomes after NCT in triple-negative
breast cancer [25], but this was not confirmed by Humbert
et al. [26]. In the former study, 98 T2-3 breast cancer patients
underwent FDG PET before treatment and after 6 8 weeks of
NCT, and FDG PET showed different predictive power in the
three molecular subtypes: HER2-positive (AUC 0.35), ER-
positive/HER2-negative (AUC 0.90) and triple-negative
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(AUC 0.96). These results in triple-negative patients have also
been confirmed in a larger series [27]. Humbert et al. exam-
ined 136 T2-3 breast cancer patients who were treated with
wide variety of chemotherapy regimens, and investigated the
levels of FDG uptake and metabolic changes after the first
cycle of NCT in patients with the same molecular subtypes.
They found that pCR has significant predictive value only in
HER2-positive breast cancer [26].In a substudy of the NEOALTTO trial in Her2-positive
breast cancer patients, Gebhart et al. found that early metabol-
ic assessment using FDG PET (2 and 6 weeks after the start of
anti-HER2 treatment) is able to identify patients with an in-
creased likelihood of pCR [28]. Increased likelihood of pCR
was associated with higherSUVmax at both time-points used
in the study. However, it is noteworthy that there was marked
heterogeneity in response in terms of FDG uptake according
to hormonal receptor status, with hormonal receptor-positive
tumours showing a significantly lower frequency of pCR.
The value of FDG as a metabolic tracer may be more af-
fected by several different molecular crosslinks and crosstalk,as well as metabolic differences in molecular breast cancer
subtypes, and especially in glycolytic metabolism [6769].
The metabolic differences among the distinct immunohisto-
chemical breast cancer subtypes has been related to specific
metabolic patterns [70].
MRI, alone or associated with FDG PET, has been also
investigated as a non-invasive technique for monitoring the
response to NCT and for assessment of residual disease. A
meta-analysis of the diagnostic performance of DW-MRI
and DCE-MRI in terms of the pathological response to NAC
in patients with breast cancer has been performed. The esti-
mated sensitivity and specificity of DW-MRI were 93 % and
82 %, respectively. In contrast, the sensitivity and specificity
of CE-MRI were 68 % and 91 % [71]. Based on these results,
t h e c o m b i n e d u s e o f D W - M R I a n d C E - M R I a s a
multiparametric evaluation has the potential to improve the
diagnostic performance in monitoring NCT. In this regard,
by applying multiparametric DCE-MRI and DW-MRI some
authors have found a sensitivity, specificity and AUC of 92 %,
78 % and 0.88, respectively, in predicting pathological re-
sp o n se after th e first cy cle o f ch emo th erap y [16 ].
Furthermore, several studies have investigated the usefulness
of MR spectroscopy for predicting response to therapy. The
discriminative value of this technique is still under investiga-
tion due to the difficulty in quantifying choline [18,19], espe-
cially following the central changes in morphology and vas-
cularity induced by chemotherapy.
More recent studies have investigated the possible value of
the combination of MRI and FDG PET [17,72, 73]. Both
techniques can provide functional information with MRI,
when evaluating angiogenesis, mainly giving information
about volume, perfusion and the permeability index, and
FDG PET reflecting the metabolic changes of breast cancer.
In particular, in a single institutional study of 93 breast cancer
patients treated with NCT, Pengel et al. showed that FDG PET
and MRI have a complementary predictive ability. Using FDG
PET and MRI together in a multivariate analysis combined
with breast cancer subtypes, the AUC was 0.90 [72].
Despite its better accuracy than conventional radiological
techniques, even MRI may encounter difficulties especially in
patients with a non-mass lesion. In these patients, there is noboundary volume at presentation and the response to ther-
apy cannot follow a concentric shrinkage, although resid-
ual disease is most likely represented by scattered foci of
enhancement [74].
Our pilot study with FLT PET was performed in a small
patient population and clearly needs to be repeated in a larger
cohort to definitively assess and validate the estimated cut-off
values and the proposed prediction rule. Further studies are
also needed to evaluate the impact of different molecular
breast cancer subtypes and subgroups with different prolifer-
ation rates, if any, on the predictive ability of FLT PET.
However, our study provided interesting results in terms ofsensitivity, specificity and AUC compared with previous stud-
ies of FDG PETand/or MRI. The preliminary findings suggest
the potential utility of PET scans for early monitoring of the
response to NCT in order to choose a therapeutic strategy with
a greater probability of efficacy rather than unexpected futility.
Conflicts of interest None.
Funding This work was supported by a grant from AssociazioneItaliana Ricerca sul Cancro (Study INT/35/10).
References
1. Fisher B, Brown A, Mamounas E, et al. Effect of preoperative che-motherapy on local-regional disease in women with operable breastcancer: findings from National Surgical Adjuvant Breast and BowelProject B-18. J Clin Oncol. 1997;15:248393.
2. Bonadonna G, Valagussa P, Brambilla C, et al. Primary chemothera-py in operable breast cancer: eight-year experience at the MilanCancer Institute. J Clin Oncol. 1998;16:93100.
3. von Minckwitz G, Raab G, Caputo A, et al. Doxorubicin with cyclo-phosphamide followed by docetaxel every 21 days compared withdoxorubicin and docetaxel every 14 days as preoperative treatment inoperable breast cancer: the GEPARDUO study of the German BreastGroup. J Clin Oncol. 2005;23:267685.
4. Gianni G, Baselga J, Eiermann W, et al. Feasibility and tolerability ofsequential doxorubicin/paclitaxel followed by cyclophosphamide,methotrexate, and fluorouracil and its effects on tumor response aspreoperative therapy. Clin Cancer Res. 2005;11:871521.
5. von Minckwitz G, Untch M, Blohmer J, et al. Definition and impactof pathologic complete response on prognosis after neoadjuvant che-motherapy in various intrinsic breast cancer subtypes. J Clin Oncol.2012;30:1796804.
6. Esserman LJ, Berry DA, DeMichele A, et al. Pathologic completeresponse predicts recurrence-free survival more effectively by cancer
828 Eur J Nucl Med Mol Imaging (2015) 42:818830
-
7/24/2019 (1)(8)F-FLT PETCT as an Imaging Tool for Early Prediction of Pathological Response in Patients With Locally Advanc
12/13
subset: results from the I-SPY 1 TRIAL-CALGB 150007/150012,ACRIN 6657. J Clin Oncol. 2012;30:32429.
7. Sataloff DM, Mason BA, Prestipino AJ, Seinige UL, Lieber CP,Baloch Z. Pathologic response to induction chemotherapy in locallyadvanced carcinoma of the breast: a determinant of outcome. J AmColl Surg. 1995;180:297306.
8. Symmans WF, Peintinger F, Hatzis C, et al. Measurement of residualbreast cancer burden to predict survival after neoadjuvant chemother-apy. J Clin Oncol. 2007;25:441422.
9 . K a u fm a n n M , H o r to b a gy i G N , G o l d h ir s c h A , e t a l .Recommendations from an international expert panel on the use ofneoadjuvant (primary) systemic treatment of operable breast cancer:an update. J Clin Oncol. 2006;24:19409.
10. Rastogi P, Anderson SJ, Bear HD, et al. Preoperative chemotherapy:updates of National Surgical Adjuvant Breast and Bowel ProjectProtocols B-18 and B-27. J Clin Oncol. 2008;26:77885.
1 1 . K au fman n M , v o n M i n ck w i t z G , M amo u n as EP , et al .Recommendations from an International Consensus Conference onthe current status and future of neoadjuvant systemic therapy inprimary breast cancer. Ann Surg Oncol. 2012;19:150816.
12. Corben AD, Abi-Raad R, Popa I, et al. Pathologic response and long-term follow-up in breast cancer patients treated with neoadjuvantchemotherapy. A comparison between classifications and their prac-tical application. Arch Pathol Lab Med. 2013;137:107482.
13. Schott AF, Roubidoux MA, Helvie MA, et al. Clinical and radiologicassessments to predict breast cancer pathologic complete re-sponse to neoadjuvant chemotherapy. Breast Cancer Res Treat.2005;92:2318.
14. OFlynn EA, Desousa NM. Functional magnetic resonance: bio-markers of response in breast cancer. Breast Cancer Res. 2011;13:20440.
15. Le-Petross HC, Hylton N. Role of breast MR imaging in neoadjuvantchemotherapy. Magn Reson Imaging Clin N Am. 2010;18:24958.
16. Li X, Abramson RG, Arlinghaus LR, et al. Multiparametric magneticresonance imaging for predicting pathological response after the firstcycle of neoadjuvant chemotherapy in breast cancer. Invest Radiol.2014. doi:10.1097/RLI.0000000000000100
17. Jacobs MA, Ouwerkerk R, Wolff AC, et al. Monitoring of neoadju-vant chemotherapy using multiparametric, 23Na sodium MR, andmultimodality (PET/CT/MRI) imaging in locally advanced breastcancer. Breast Cancer Res Treat. 2011;128:11926.
18. Manton DJ, Chaturvedi A, Hubbard A, et al. Neoadjuvant chemo-therapy in breast cancer: early response prediction with quantitativeMR imaging and spectroscopy. Br J Cancer. 2006;94:42735.
19. Meisamy S, Bolan PJ, Baker EH, et al. Neoadjuvant chemotherapyoflocally advanced breast cancer: predicting response with in vivo 1HMR spectroscopy a pilot study at 4 T. Radiology. 2004;233:42431.
20. Cochet A, Generali D, Fox SB, Ferrozzi F, Hicks RJ. Positron emis-sion tomography and neoadjuvant therapy of breast cancer. J NatlCancer Inst Monogr. 2011;43:1115.
21. Barriolo-Riedinger A, Touzery C, Riedinger JM, et al. [18F]FDG-PET predicts complete pathological response of breast cancer to neo-adjuvant chemotherapy. Eur J Nucl Med Mol Imaging. 2007;34:
1915
24.22. Duch J, Fuster D, Munoz M, et al. 18F-FDG PET/CT for early pre-diction of response to neoadjuvant chemotherapy in breast cancer.Eur J Nucl Med Mol Imaging. 2009;36:15517.
23. Groheux D, Giacchetti S, Hatt M, et al. HER2-overexpressing breastcancer: FDG uptake after two cycles of chemotherapy predicts theoutcome of neoadjuvant treatment. Br J Cancer. 2013;109:115764.
24. Groheux D, Hindie E, Giacchetti S, et al. Early assessment with 18F-fluorodeoxyglucose positron emission tomography/computed to-mography can help predict the outcome of neoadjuvant chemothera-py in triple negative breast cancer. Eur J Cancer. 2014;50:186471.
25. Koolen BB, Pengel KE, Wesseling J, et al. FDG PET/CT duringneoadjuvant chemotherapy may predict response in ER-positive/
HER2-negative and triple negative, but not in HER2-positive breastcancer. Breast. 2013;22:6917.
26. Humbert O, Berroilo-Riedinger A, Riedinger JM, et al. Changes in18F-FDG tumor metabolism after a first course of neoadjuvant che-motherapy in breast cancer: influence of tumor subtypes. Ann Oncol.2012;23:25727.
27. KoolenBB, PengelKE, Wesseling J, et al. Sequential 18F-FDG PET/CT for early prediction of complete pathological response in breastand axilla during neoadjuvant chemotherapy. Eur J Nucl Med Mol
Imaging. 2014;41:3240.28. Gebhart G, Gamez C, Holmes E, et al. 18F-FDG PET/CT for early
prediction of response of neoadjuvant lapatinib, trastuzumab, andtheir combination in HER2-positive breast cancer: results fromNeo-ALTTO. J Nucl Med. 2013;54:18628.
29. Andrade WP, Lima ENP, Osorio CABT, et al. Can FDG-PET/CTpredict early response to neoadjuvant chemotherapy in breast cancer?Eur J Surg Oncol. 2013;39:135863.
30. Salskov A, Tammisetti VS, Grierson J, Vesselle H. FLT: measuringtumor cell proliferation in vivo with positron emission tomographyand 3-deoxy-3-18F-fluorothymidine. Semin Nucl Med. 2007;37:42939.
31. Rasey JS, Grierson JR, WiensLW, et al. Validationof FLT uptake as ameasure of thymidine kinase-1 activity in A549 carcinoma cells. JNucl Med. 2002;43:12107.
32. Been LB, Suurmeijer AJ, Cobben DCP, Elsinga PH, de Vries J, et al.[18F]FLT-PET in oncology: current status and opportunities. Eur JNucl Med Mol Imaging. 2004;31:165972.
33. Pio BS, Park CK, Pietras R, et al. Usefulness of 3-[F-18]fluoro-3-deoxythymidine with positron emission tomography in predictingbreast cancer response to therapy. Mol Imaging Biol. 2006;8:3642.
34. Kenny L, Coombes RC, Vigushin DM, Al-Nahhas A, Shousha S,Aboagye EO. Imaging early changes in proliferation at 1 week postchemotherapy: a pilot study in breast cancer patients with 3 -deoxy-3-18F-fluorothymidine positron emission tomography. Eur J NuclMed Mol Imaging. 2007;34:133947.
35. Contractor KB, Kenny LM, Stebbing J, et al. [18F]-3 deoxy-3-fluorothymidine positron emission tomography and breast cancerresponse to docetaxel. Clin Cancer Res. 2011;17:766472.
36. Woolf DK, Beresford M, Li SP, et al. Evaluation of FLT-PET-CT asimaging biomarker of proliferation in primary breast cancer. Br JCancer. 2014;110:284754.
37. Pascali C, Bogni A, Fugazza L, et al. Simple preparation and purifi-cation of ethanol-free solutions of 3'-deoxy-3'-[18F]fluorothymidineby means of disposable solid-phase extraction cartridges. Nucl MedBiol. 2012;39:54050.
38. Smyczek-Gargya B, Fersis N, Dittmann H, et al. PET with[18F]fluorothymidine for imaging of primary breast cancer: a pilotstudy. Eur J Nucl Med. 2004;31:7204.
39. The University of Texas MD Anderson Cancer Center. Residual can-cer burden calculator. http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3. Accessed 29 Jan 2015.
40. Elston CW, Ellis IO. Pathological prognostic factors in breast cancer.I. The value of histological grade in breast cancer: experience from a
large study with long-term follow-up. Histopathology. 1991;19:403
10.41. Goldhirsch A, Winer EP, Coates AS, et al. Personalizing the treat-
ment of women with early breast cancer: highlights of the St GallenInternational Expert Consensus on the Primary Therapy of EarlyBreast Cancer 2013. Ann Oncol. 2013;24:220623.
42. Farwell MD, Pryma DA, Mankoff DA. PET/CT imaging in cancer:current applications and future directions. Cancer. 2014;120:343345.
43. Schwartz JL, Tamura Y, Jordan R, Grierson JR, Krohn KA.Monitoring tumor cell proliferation by targeting DNA synthetic pro-cesses with thymidine and thymidine analogs. J Nucl Med. 2003;44:202732.
Eur J Nucl Med Mol Imaging (2015) 42:818830 829
http://dx.doi.org/10.1097/RLI.0000000000000100http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3http://www3.mdanderson.org/app/medcalc/index.cfm?pagename=jsconvert3http://dx.doi.org/10.1097/RLI.0000000000000100 -
7/24/2019 (1)(8)F-FLT PETCT as an Imaging Tool for Early Prediction of Pathological Response in Patients With Locally Advanc
13/13
44. Kenny LM, Vigushin DM, Al-Nahhas A, et al. Quantification ofcellular proliferation in tumor and normal tissues of patients withbreast cancer by 18F-fluorothymidine-positron emission tomographyimaging: evaluation of analytical methods. Cancer Res. 2005;65:1010412.
45. Buck AK, Bommer M, Stilgenbauer S, et al. Molecular imaging ofproliferation in malignant lymphoma. Cancer Res. 2006;66:1105561.
46. YamamotoY, Nishiyama Y, Ishikawa S, et al. Correlation of 18F-FLTand 18F-FDG uptake on PET with Ki-67 immunochemistry in non-
small cell lung cancer. Eur J Med Mol Imaging. 2007;34:16106.47. Chalkidou A, Landau DB, Odell EW, et al. Correlation between Ki-
67 immunohistochemistry and 18F-Fluorothymidine uptake in pa-tients with cancer: a systematic review and meta-analysis. Eur JCancer. 2012;48:3499513.
48. Dittmann H, Dohmen BM, Paulsen F, et al. [18F]FLT PET for diag-nosis and staging of thoracic tumours. Eur J Nucl Med Mol Imaging.2003;30:140712.
49. Buck AK, Halter G, Schirrmeister H, et al. Imaging proliferation inlung tumors with PET: 18F-FLT versus 18F-FDG. J Nucl Med.2003;44:142631.
50. Hoshikawa H, Nishiyama Y, Kishino T, et al. Comparison of FLT-PET and FDG-PET for visualization of head and neck squamous cellcancers. Mol Imaging Biol. 2011;13:1727.
51. Kameyama R, Yamamoto Y, Izuishi K, et al. Detection of gastriccancer using 18F-FLT PET: comparison with 18F-FDG PET. Eur JNucl Med Mol Imaging. 2009;36:3828.
52. Chen W, Cloughesy T, Kamdar N, et al. Imaging proliferation inbrain tumors with 18-FLT PET: comparison with 18F-FDG. J NuclMed. 2005;46:94552.
53. van Westreenen HL, Cobben DCP, Jager PL, et al. Comparison of18F-FLT PET and 18F-FDG in esophageal cancer. J Nucl Med.2005;46:4004.
54. van Waarde A, Cobben DC, Suurmeijer AJ, et al. Selectivity of 18F-
FLTand 18F-FDG for differentiating tumour from inflammation in arodent model. J Nucl Med. 2004;45:695700.
55. Kenny LM, Al-Nahhas A, Aboagye EO. Novel PET biomarkers forbreast cancer imaging. Nucl Med Commun. 2011;32:3335.
56. Lubberink M, Direcks W, Emmering J, et al. Validity of simplified 3-deoxy-3-[18F]fluorothymidine uptake measures for monitoring re-sponse to chemotherapy in locally advanced breast cancer. MolImaging Biol. 2012;14:77782.
57. Kinahan PE, Fletcher JW. Positron emission tomography-computedtomography standardized uptake values in clinical practice andassessing response to therapy. Semin Ultrasound CT MRI. 2010;31:496505.
58. Eckel F, Herrmann K, Schmidt S, et al. Imaging of proliferation inhepatocellular carcinoma with the in vivo marker 18F-fluorothymidine. J Nucl Med. 2009;50:14417.
59. Buck AK, Schirrmeister H, Hetzel M, et al. 3-deoxy-3-[(18)F]fluorothymidine-positron emission tomography for noninva-sive assessment of proliferation in pulmonary nodules. Cancer Res.2002;62:33314.
60. Vesselle H, Grierson J, Muzi M, et al. In vivo validation of 3-deoxy-3-18F-fluorothymidine (18F-FLT) as a proliferation imaging tracer inhumans: correlation of 18F-FLT uptake by positron emission tomog-raphy with Ki-67 immunohistochemistry and flow cytometry in hu-man lung tumors. Clin Cancer Res. 2002;8:331523.
61. Wang Y, Zhang C, Liu J, Huang G. Is 18F-FDG PET accurate topredict neoadjuvant therapy response in breast cancer? A meta-anal-ysis. Breast Cancer Res Treat. 2012;131:35769.
62. Cortazar P, Zhang L, Untch M, et al. Pathological complete responseand long-term clinical benefit in breast cancer: the CTNeoBC pooledanalysis. Lancet. 2014;384:16472.
63. Provenzano E, Vallier A-L, Champ R, et al. A central review ofhistopathology reports after breast cancer neoadjuvant chemotherapyin the neo-tango trial. Br J Cancer. 2013;108:86672.
64. Ogston KN, Miller ID, Payne S, et al. A new histologic gradingsystem to assess response of breast cancers to primary chemotherapy:prognostic significance and survival. Breast. 2003;12:3207.
65. Chollet P, Abrial C, Durando X, et al. A new prognostic classificationafter primary chemotherapy for breast cancer: residual disease inbreast and nodes (RDBN). Cancer J. 2008;14:12832.
66. Marchi C, Sapino A. The pathologic complete response open ques-tion in primary therapy. J Natl Cancer Inst Monogr. 2011;43:8690.
67. Kim S, Kim DH, Jung WH, et al. Metabolic phenotypes in triple
negative breast cancer. Tumor Biol. 2013;34:1699
712.68. Kim SK, Jung WH, Koo JS. Differential expression of enzymes
associated with serine/glycine metabolism in different breast cancersubtypes. PLoS One. 2014;9:e101004.
69. Kajari K, Tokes T, Dank M, et al. Correlation of the value of 18F-FDG uptake, described by SUVmax, SUVavg, metabolic tumourvolume and total lesion glycolysis, to clinicopathological prognosticfactors and biological subtypes in breast cancer. Nucl Med Commun.2015;36:2837.
70. Vicente G, Castrejon AS, Leon MA, et al. Molecular subtypes ofbreast cancer: metabolic correlation with 18F-FDG PET/CT. Eur JNucl Med Mol Imaging. 2013;40:130411.
71. Wu L, Hu J, Gu H, et al. Can diffusion weighted MR imaging andcontrast-enhanced MR imaging precisely evaluate and predict path-ological response to neoadjuvant chemotherapy in patients with
breast cancer? Breast Cancer Res Treat. 2012;135:1728.72. Pengel KE, Koolen BB, Loo CE, et al. Combined use of 18F-FDG
PET/CT and MRI for response monitoring of breast cancer duringneoadjuvant chemotherapy. Eur J Nucl Med Mol Imaging. 2014;41:151524.
73. Partridge SC, Vanantwerp RK, Doot RK, et al. Association betweenserial dynamic contrast enhanced MRI and dynamic 18F-FDG PETmeasures in patients undergoing neoadjuvant chemotherapy for lo-cally advanced breast cancer. J Magn Reson Imaging. 2010;32:112431.
74. BahriS, Chen J, Mehta RS, et al.Residual breast cancer diagnosed byMRI in patients receiving neoadjuvant chemotherapy with and with-out bevacizumab. Cancer. 2009;16:161928.
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