Definition
A rare malignant tumour arising in soft tissue in children, analogous to myoepithelial carcinoma of the salivary gland, breast, upper aerodigestive tract and skin. Myoepithelial differentiation is demonstrated by positivity for cytokeratins or EMA, and for one of S100, GFAP, SMA or HHF35.
The lesion may occur at any age in childhood, including congenitally. There is no gender predominance.
The tumour may occur at a wide range of sites, with half of all cases on the extremities. Half the cases are subcutaneous, others being visceral or in deep soft tissue, rarely intradermal.
Tumours are usually well demarcated, often with a thin capsule but deep tumours may be infiltrative. The cut surface are variably white, tan, fleshy, gelatinous, haemorrhagic or focally calcified. There may be focal necrosis.
The criteria for malignancy are cytological, that is at least moderate cytological atypia. A benign precursor lesion is rare.
At low power there is often a lobular architecture. Cellularity is often greater at the periphery of lobules with cells forming trabecular, nests or solid sheets. The cells are variably epithelioid, clear, spindled or plasmacytoid; almost always more than one cell type is present. The mitotic rate is very variable. The stroma is myxoid or hyalinised, sometimes with cartilaginous differentiation. Rarely there is metastatic ossification.
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14/211 |
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15/201 |
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17/181 |
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29/291 |
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1/71 |
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21/291 |
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15/281 |
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25/291 |
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3/51 |
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7/111 |
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0/121 |
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1/141 |
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0/111 |
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6/71 |
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Myoepithelial carcinoma metastatic from salivary gland, bronchus or breast, but tumour at these sites is rare in children.
Epithelioid sarcoma: has a diffusely infiltrative growth pattern with a densely collagenous stroma; usually negative for S100, GFAP and INI-1. May be positive for CD34.
Synovial sarcoma: lacks a lobular architecture. GFAP is negative. There is a characteristic t(X;18) translocation.
Extraskeletal myxoid chondrosarcoma: comprises lobules of spindle cells within a myxoid stroma. Lacks cytoloical atypia except in high-grade cases. GFAP and cytokeratins are negative. There is typically a translocation involving 9q22.
Epithelioid malignant peripheral nerve sheath tumour: uncommon in children; shows a lobular architecture. S100 and GFAP are positive. Rarely positive for cytokeratins.
Ewing's sarcoma/PNET: sometimes positive for cytokeratins and S100, but not for other myoepithelial markers. Shows diffuse membranous positivity for CD99.
Extrarenal rhabdoid tumour; occurs only in children; is composed solely of uniform large polygonal cells with eccentric nuclei and prominent nucleoli.
Metastatic carcinoma.
Has been by various combinations of surgery and chemotherapy.
50% of patients develop local recurrence despite complete resection. 50% develop metastases, to lungs, lymph nodes, bone and other sites. Nearly half the patients die of disease. Tumour size and tumour necrosis predict death form disease. Patient age, site and mitotic activity do not correlate with prognosis.
This page last revised 6.3.2008
©SMUHT/PW Bishop