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 × 13 × 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∼p34, 1q21∼q23, 9q12∼q33, and 16q22 and losses of 1p11∼p22, 1q24∼q44, 3p, 10q11.1∼q22, 13q, 14q13∼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.