Malignant myoepithelioma of soft tissue: a case report with cytogenetic findings

Soft tissue malignant myoepithelioma (STMM) is a particularly rare tumor displaying myoepithelial elements and lacking obvious ductal differentiation. From the one case report with cytogenetic data available in the literature, STMM seems to be a distinct entity with some resemblance to chordoma on the one hand and myoepithelioma on the other. The present case of STMM yielded novel data from high-resolution comparative genomic hybridization (HR-CGH) analysis. An 82-year-old female patient presented with a soft tissue tumor within the deep soft tissues in the right gluteal muscle measuring 16 x 13 x 11 cm. Histologically, the lesion was diagnosed as a myoepithelial carcinoma. Immunohistochemistry was focally positive for pancytokeratin, EMA, S-100 protein, and alpha smooth muscle actin. HR-CGH analysis revealed gains of 1p31 approximately p34, 1q21 approximately q23, 9q12 approximately q33, and 16q22 and losses of 1p11 approximately p22, 1q24 approximately q44, 3p, 10q11.1 approximately q22, 13q, 14q13 approximately q24, and 15q. Subsequent fluorescence in situ hybridization analysis confirmed deletion of 3p, gain of 16q, and monosomy of chromosomes 13 and 15. These results support the hypothesis that STMM is a distinct entity, not sharing the cytogenetic alterations of salivary gland myoepithelial carcinomas and ductal carcinomas of breast with myoepithelial differentiation.