Malignant myoepithelioma of the vulva resembling a rhabdoid tumour

Aims We report an example of malignant myoepithelioma of the vulva, which has not been hitherto described. We discuss the differential diagnosis and briefly review the literature. Methods and results The lesion was found in an 81‐year‐old woman as an indolent 40 mm tumour. The neoplastic cells showed a myoid, spindled, epithelioid and plasmacytoid phenotype. Hyalinization of extracellular material and myxoid changes were present. There was a partly solid and microcystic pattern and a tight cohesiveness of cells was lacking. The circumscribed multinodular tumour somewhat resembled an extrarenal rhabdoid tumour, having large tumour cells with prominent nucleoli and large amounts of acidophilic cytoplasm. Immunohistochemically, the tumour cells were immunoreactive for cytokeratin, vimentin, muscle‐specific actin, alpha‐smooth muscle actin, and S100 protein, but not for desmin, epithelial membrane antigen, factor VIII‐related antigen, CD34 and CD31. Conclusions The histological and cytomorphological appearance of the tumour well as the immunohistochemical findings suggest the diagnosis of malignant myoepithelioma, possibly derived from minor vestibulary glands or ectopic breast tissue. Differential diagnoses are, in particular, extrarenal rhabdoid tumour and ‘proximal type’ epithelioid sarcoma. Differentiation is important, because the tumours show a different behaviour and prognosis.