Hum Genet (1983) 64 : 257-262

© Springer-Verlag 1983

Chromosome abnormalities in chronic myeloid leukemia in children

G. P. Puchkova, E. L. Prigogina, E. W. Fleischmann, T. S. Drosdova, S. A. Mayakova, and I. S. Peterson

Laboratory of Cytogenetics, Cancer Research Center, AMS USSR, Kashirskoye shosse 24, Moscow 115 478, USSR

Summary. Banded chromosomes of leukemic ceils were studied in 53 children with chronic myeloid leukemia (CML). Ph ~ chromosome was found in 21 children, and the remaining 32 cases were Ph ~ negative. Besides Ph ~ translocation additional chromosomal abnormalities, including marker i(17q), were revealed in three of eight children studied in blastic crisis of Ph 1 positive CML.

Leukemic cells of most patients with Ph 1 negative CML possessed normal karyotype. Clones with chromosomal abnor- malities were found in 12 of 32 cases. Most characteristic were monosomy 7 (in four chidren) and trisomy 8 (in three). Abnormal karyotype may be a bad prognostic sign in Ph ~ negative CML. The presented data confirm the difference in age of appearance, bone marrow pattern and clinical course between Ph ~ positive ("adult") and Ph I negative (juvenile) types of CML in children. Probable prenatal commencement of CML in babies and children in the first years of life is discussed.

Introduction

Chronic myeloid leukemia (CML) is rare in children. It accounts for 2-7% of all childhood leukemias. Two variants, differing in clinical manifestations, are observed: "adult", Ph 1 positive, and juvenile, Ph 1 negative (Hardisty et al. 1964; Smith and Johnson 1974). The karyotype of leukemic cells in childhood CML has been insufficiently studied, mostly without banding. Herein we present the results of chromosome banding performed in 53 children with CML.

Materials and methods

Karyotype of leukemic cells was studied in 53 children aged from 16 days to 14 years. There were 34 boys and 19 girls. Bone marrow specimens or blood and marrow cells were analyzed in 46 patients and peripheral blood cells only in seven. Blood and marrow cells were studied after 24-48 h cultivation (without PHA stimulation). In 34 cases cytogenetic study was done prior to treatment, in the others after commencing chemotherapy. In most patients cytogenetic study was performed only once, since many children came to the Cancer Research Center for diagnosis and were treated and followed elsewhere. The data on survival were obtained in such cases from the patients' physicians by post. The trypsin-Giemsa method was used for G-banding. Karyo- typing was performed according to the International System for Human Cytogenetic Nomenclature (ISCN 1978).

Offprint requests to: G. P. Puchkova

Results

Phi positive CML. This was diagnosed in 21 patients. Main clinical and laboratory data on these patients are summarized in Table 1, and the results of cytogenetic study in Table 2. Only one of the children in this group was less than 1 year old, seven were aged from 1 to 5 years, and 13 were aged from 7 to 14 years old. On the day of study (which in ten children was close to the day of diagnosis) the following were noted in most children: elevated WBC counts with a shift to the left, spleen enlargement and increased marrow cellularity with prevalence of granulocytic lineage. Fifteen patients were studied in the chronic phase of CML, four in blastic crisis (16, 19, 20, and 21), and three in remission of blastic crisis (12, 17, 18). Four patients were studied in chronic and in acute stages (2, 9, 16, 17). Eleven of the 21 patients died during the observation period. In two of these the disease was recognized only in the terminal stage (patients 18 and 19). These children survived 1 and 3 months after diagnosis. Median survival of the deceased was 36.3 months. Ten patients are alive 2-25 months after diagnosis, and six of these are now in the terminal stage of the disease.

Regular translocation t(9;22)(q34;qll) was observed in 19 children, atypical t(2;22)(q37;q11) in one (Fig. l) and in another a complex translocation involving chromosomes 5, 9 and 22: t (5;9;22) (q31 ;q34;ql 1) (Fig. 2). In blastic crisis three of eight patients studied had characteristic abnormalities, most commonly seen in this stage of CML: marker i (17q) was found in all of them, and was accompanied by trisomy 8 in one patient and by additional chromosomes 8 and 19 in another (cases 19, 20, 21) (Fig. 3). Additional abnormalities were not revealed in a further five terminal stage patients.

Ph~ negative CML (see Tables 1 and 2). Thirty-two patients were studied; nine were aged less than 1 year including seven under 6 months; 15 were 1-5 years old and eight were aged 6-14 years. Characteristic symptoms at diagnosis were moderate or high leucocytosis with a shift to the left and in most cases with elevated monocyte counts, thrombocytopenia, hemorrhagic syndrome manifestations, and significant spleen and liver enlargement. Blast cell counts in blood and/or marrow were elevated on the day of study in 21 patients: 5-16% in 12, 20-89% in 9. In the latter nine patients diagnosis of blastic crisis was established.

Of the 26 patients followed up, seven are alive 1-28 months after diagnosis (five are now in blastic crisis) and 19 died after surviving 0.5-16 months after diagnosis (median survival for the deceased was 5.9 months).

In 16 patients cytogenetic study revealed only karyotypically normal cells. In four children single cells with an aneuploid

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chromosome set were found. In three of these cases abnormal cells possessed trisomy 20. In the fourth one a small additional chromosome had a different appearance in four hyperdiploid cells.

Abnormal clones were observed in 12 patients. The size of these clones varied from 10 to 100% of the cell population. In three patients abnormal clones were hypodiplid, in five pseudodiploid, and in four hyperdiploid. Among patients with abnormal karyotype four had monosomy 7 and three trisomy 8 (Figs. 4 and 5). In other patients abnormal clones possessed the following karyotypes: 46,XY,-18,+mar; 47,XX,-9,+22,+mar; 46,XY,der(11); 46,XY,20q-; 46,XY,t(6;9)(p23;q34).

In 10 of the 12 patients with abnormal karyotype, cells with a normal chromosome set were also present in the marrow where they constituted 3-90% of all cells.

Discussion

The presented data confirm the existence of distinct difference between two forms of CML in children. Our patients with juvenile CML were much younger than those with the adult form: 9 of 32 versus 1 of 21 before 1 year and 8 of 32 versus 13 of 21 aged 6 years and older respectively. Leucocytosis was not so high in juvenile as in adult form. Anaemia, thrombocytopenia with manifestations of hemorrhagic syndrome, pronounced

monocytosis, and elevated marrow blast counts at diagnosis were the other characteristics of the juvenile form. The latter trait, as well as spleen and liver enlargement, rapid course of the disease, and absence of Ph 1 chromosome in bone marrow cells, caused difficulties in differential diagnosis and hindered the staging of juvenile CML. The treatment of juvenile CML was unsuccessful and median survival was very short; only 5.9 months. Median survival in Ph 1 positive CML was significantly longer--36.3 months.

Cytogenetic study revealed the Ph ~ translocation in 21 children. In two of them this translocation was atypical: t (2;22) in one child and t(5;9;22) in the other. Probably the frequency of atypical Ph I translocations in children does not differ greatly from that in adults, where atypical translocations are discovered in 5-10% of the cases (Sandberg 1980; Fleischman et al. 1981).

The finding of characteristic additional chromosomal abnor- malities [i(17q),+8,+ 19] in three of our patients studied in blastic crisis suggests that the main pathway of karyotype evolution in CML is the same in adults and in children. As in our adult CML patients the marker i(17q) was revealed in cases with distinct signs of myeloid differentiation of blast cells (granular cyto- plasm, peroxidase positivity).

In juvenile CML the karyotype of blood and marrow cells was Ph ~ negative and in most cases normal. However, abnormal clones were revealed in 11 patients and single aneuploid cells in four Other children. Among patients with abnormal cell clones four had monosomy 7 and three trisomy 8. Both of these abnormalities are often met in various myeloproliferative disorders: myelofibrosis, refractory anaemia, acute nonlympho- cytic leukemia (ANLL) and blastic crisis of Ph 1 positive CML (Berghe et al. 1979; Sandberg 1980). The frequency of these karyotype anomalies in different entities is not yet established. It should be mentioned that monosomy 7 in ANLL and in preleukemia is regarded as a poor prognostic sign (Borgstrom et al. 1980; Sief et al. 1981).

We found in the literature results from a cytogenetic study of 103 patients with juvenile CML. Chromosome abnormalities

26O

Table 2. Cytogenetic data

Patients Source a Metaphases investigated (no.) banded/total

Cells with normal karyo- type (%)

Karyotype

1 BM 31/71

2 BM 23/80

3-18 BM 179/406 PB 48/147

19 PB 20/40

20 PB 25/25

21 PB 20/55

m

m

B

F

46,XY,t (2;22)(q37;ql 1)

46,XX,t (5 ;9;22) (q31 ;q34;q 11 )

46,XX or XY,t(9;22)(q34;ql 1)

46,XY,t (9;22)(q34;ql 1),i(17q)

46,X X,t (9 ;22) (q34;q 1 ] ),i ( 17q)/ 47 ,XX,t (9 ;22) (q34;q 11 ),i ( 17q),+ 8

46,XY,t (9;22)(q34;ql 1),i(17q)/ 47,XY,t(9;22)(q34;ql 1),i(17q),+8/ 50,XY,t(9;22)(q34;qll),i(17q),+8,+19,+21,+22

22-37 b BM 132/487 100 46,XX or XY PB 100/208

38 BM 20/50 99 47,XX,+20(1) c

39 BM 25/72 99 47,XX,-7,+20,+21 (1)

40 BM 20/90 99 48,XY,+C(8?),+20 (1)

41 BM 15/37 97 47,XX,+mar(2) PB 16/27 97 47,XX,+G(2)

42 BM 34/70 94 46,XY,20q+

43 BM 11/11 100 46,XY PB 27/72 93 46,XY,- 18,+mar

44 BM 41/68 - - 46,XY,t (6;9) (p23;q34) PB 7/7 - - 46,XY,t (6;9) (p23;q34)

45 BM 30/30 63 46,XY,der (11)

46 BM 22/38 70 47,XX,-9,+22,+mar

47 BM 6/49 16 45,XX,-7 PB 6/21 38 45,XX,-7

48 BM 21/71 3 45,XY,-7 PB 20/40 3 45,XY,-7

49 BM 11/54 28 45,XY,-7

50 BM 9/19 - - 46,XY,-7,+21/54,XY,-7,... +21(1)

51 BM 27/88 7 47,XX,+8 PB 10/10 0 47,XX,+8

52 BM 18/18 10 47,XX,+8

53 BM 42/109 84 47,XX,+8 (13)/ 54,XX,+8,+9,+ 13,+ 18,+ 19,+21,+22,+C(5)

a BM ' bone marrow, PB, peripheral blood; b including one patient with Down's syndrome; c in parentheses, the number of cells with the given abnormality

were revealed in 19 cases but only in nine of them was chromosome banding performed. Monosomy 7 was revealed in two of these nine patients (Symann et al. 1982), loss of Y chromosome in one (Hays et al. 1979) and different chromosome rearrangements in six (Altman et al. 1974; Brodeur et al. 1979; Casalone et al. 1981; Inoue et al. 1977; Srivastava et al. 1981; Warburton and Shah 1976). Thus, various chromosomal abnormalities may be seen in juvenile CML. We assumed earlier that there are correlations between karyotype abnormalities and clinical and morphological manifestations of Ph 1 positive CML (Prigogina et al. 1978; Fleisehman et al. 1981). Further studies are needed to find out if such correlations may be outlined in juvenile CML as well. Now we can mention only that in children with normal karyotype, survival was a little longer (1-28 months,

median 7.6 months) than in juvenile CML patients having chromosomal abnormalities (1-9 months, median 4.8 months).

Recognition of CML in babies and in children in the first years of life allows discussion of which cases must be considered as congenital leukemia. We feel that appearance of acute and especially chronic leukemia in the first months and even in the first years after birth is possible only in cases with prenatal commencement of the disease. Estimating the probable duration of the latent period in leukemia, one has to take into account that malignant cells are proliferating no faster (and rather slower) than their normal bone marrow counterparts (Astaldi and Mauri 1953; Clarkson 1969, 1981) and that clinical manifestations of leukemia arise when the number of malignant cells reaches approximately 1012 (Clarkson 1981). That usually needs several

261

Fig. 1. Atypical Ph I translocation in patient G.A. (case 1): 46,XY, t (2;22) (q37 ;q 11)

Fig.2. Complex Ph 1 translocation in case 2 (patient K.E.): 46,XX, t (5;9;22)(q31;q34;ql 1)

Fig. 3. Marrow cell of patient U.A., case 21 (blastic crisis): 47,XY,t (9;22) (q34;ql I),+8,i(17q)

262

References

Fig. 4. Karyotype of patient L.E., marrow cell (case 48): 45,XY,-7

Fig. 5. Trisomy 8 in the marrow cell of patient A.E. (case 5 I): 47,XX,+8

years. Kamada and Uchino (1978) published the results of a long term follow-up of a large group of people surviving an atomic explosion. Systematic blood and marrow control and the study of proliferation rate of leukemic cells in some of the 16 patients developing CML allowed the authors to conclude that the first Ph 1 positive cells appeared in these patients nearly 6.3 years prior to clinical manifestations of CML.

The rate of proliferation of leukemic cells is subject to significant individual variations, and it may be especially high in the prenatal and postnatal periods of life. Detection of Ph 1 positive CML in a 10-month-old baby (our case) and in five other babies (Sandberg 1980) witness that the median duration of latency in CML may be significantly shorter than 6.3 years (median duration of latency given by Kamada and Uchino). However, a long latent period, lasting from several months to several years, evidently precedes recognition of CML. In this aspect all cases of CML in babies and children in the first years of life have to be considered as inborn.

Acknowledgements. The authors are grateful to Professor H. E. Pogo- sianz for help and valuable advice and to Professor L. A. Machonova for discussion of clinical data.

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Received March 23, 1983