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Myoepithelioma of
Bone and Soft Tissue
E. Rosenberg, M.D. Andrew
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Myoepithelioma of
Bone and Soft Tissue
E. Rosenberg, M.D. Andrés
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Myoepithelioma
Definition: A neoplasm that demonstrates a myoepithelial phenotype
Myoepithelial cell: A normal cell located within an ductal acinar structures located between the lining epithelial cell and the underlying basement membrane. Demonstrate the ultrastructural and immunohistochemical features of an epithelial cells with some characteristics of smooth muscle.
Neoplasms with Myoepithelial Cells: Mixed tumors (salivary gland, skin) Myoepithelioma (salivary gland, soft tissue, bone, breast)
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Myoepithelioma
Definition: A neoplasm that demonstrates a myoepithelial phenotype
Myoepithelial cell: A normal cell located within an ductal acinar structures located between the lining epithelial cell and the underlying basement membrane. Demonstrate the ultrastructural and immunohistochemical features of an epithelial cells with some characteristics of smooth muscle.
Neoplasms with Myoepithelial Cells: Mixed tumors (salivary gland, skin) Myoepithelioma (salivary gland, soft tissue, bone, breast)
p63
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Myoepithelial Neoplasms
Myoepithelioma Mixed Tumor
Morphology
Presence of
ductal structures
Genetics Rearrangement of
PLAG1 or HMGA2
- Salivary gland
Rearrangement of
EWSR1- soft tissue
Spindle, plasmacytoid,
epithelioid, clear cells,
Myxoid or hyalinized
stroma
Immunophenotype Keratin, EMA, S-100,
GFAP, P63, calponin,
SMA, desmin
Keratin, EMA, S-100,
GFAP, P63, calponin,
SMA, desmin
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Myoepithelioma -
Clinical Features
Equal gender distribution
Wide age range
Peak incidence in 4th decade
Usually painless mass - soft tissue; pain - bone
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Myoepithelioma -
Anatomic Distribution
Soft Tissue - Subcutaneous >> deep
Limbs/limb girdles 75%
Head and neck 15%
Trunk 10%
Bone
Axial skeleton 60%
Long bones – tibia 30%
Jaw bones 10%
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Myoepithelioma –
Macroscopic Features
Most tumors 2-5 cm
Occasionally >10 cm
Grossly well-circumscribed
Glistening/gelatinous
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Myoepithelioma
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Myoepithelioma
16 year old female 31 year old female
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49 year old male
Myoepithelioma
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Myoepithelioma –
Histologic Features
Heterogeneous – similar to salivary
gland lesions
Typically lobulated/multinodular
Often reticular
Myxoid stroma common
Occasionally solid
Often mixed patterns
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Myoepithelioma –
Histologic Features
Epithelioid, spindled,
plasmacytoid
(hyaline),
or clear cells
Often mixed cell types
Metaplastic cartilage/bone
in 15%
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Myoepithelioma
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S100 SMA
EMA Ki-67
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Myoepithelioma -
Immunohistochemical Features
Keratins 60%
S-100 protein 85%
EMA 60%
GFAP 50%
Calponin 50%
SMA 40%
p63 20%
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Myoepithelioma –
Genetics
45% have rearrangement of EWSR1
EWSR1 – POU5F1 (8%) t(6;22) – clear cells
EWSR1 – PBX1 (8%) t(1;22) – clear cells, epithelioid
EWSR1 – ZNF444( 1.5%) t(19;22) – epithelioid/clear/
spindle
EWSR1 negative tumors are more often benign
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45 year old woman
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Myoepithelioma: - Criteria for
Malignancy
Nuclear atypia
Mitotic activity
Necrosis
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Malignant Myoepithelial Tumors
Soft tissue – children; bone - adults
Similar morphologic and
immunophenotypic features
May contain an undifferentiated round
cell component
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Malignant Myoepithelioma
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Malignant Myoepithelioma
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keratin
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Myoepithelial Tumors –
Clinical Behavior
Sites of metastasis: lung, lymph nodes, bone, brain, soft tissue
Diagnosis Recurrence Metastasis
Myoepithelioma 20% Rare
Myoepithelial carcinoma 40% 40-50%
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Myoepithelial Tumors -
Differential Diagnosis
Ossifying fibromyxoid tumor
Epithelioid schwannoma
Chondromyxoid fibroma
Extraskeletal myxoid chondrosarcoma
Epithelioid MPNST
Metastatic carcinoma
Proximal-type epithelioid sarcoma
Conventional chondrosarcoma
Ewing sarcoma
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Extraskeletal Myxoid
Chondrosarcoma
Distinctive rare myxoid sarcoma
Usually arise in deep soft tissues
Proximal extremities (thigh), trunk
High rate of lung metastasis (late)
NOT cartilaginous
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Extraskeletal Myxoid
Chondrosarcoma
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Chondromyxoid Fibroma
<1% of primary bone tumors
75% younger than 30 years
pain / swelling
75% involve lower extremity
95% centered in metaphysis
Ilium / metatarsal
30%
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Myoepithelioma
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Myoepithelial Tumors of
Bone and Soft Tissue
Uncommon tumor
Benign > malignant
Morphologic heterogeneity
Express keratin, EMA, S100, SMA
50% have rearrangement of
EWSR1
Treatment is complete excision