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 ind olent 40mm tumour. The neoplastic cells showed a myoid, spindled, epithelio id and plasmacytoid phenotype. Hyalinization of extracellular material and myxoid changes were present. There was a partly solid and microcystic patte rn and a tight cohesiveness of cells was lacking. The circumscribed multino dular tumour somewhat resembled an extrarenal rhabdoid tumour, having large tumour cells with prominent nucleoli and large amounts of acidophilic cyto plasm. Immunohistochemically, the tumour cells were immunoreactive for cyto keratin in, vimentin, muscle-specific actin, alpha-smooth, muscle actin, an d S100 protein, but not for desmin, epithelial membrane antigen, factor VII I-related antigen, CD34 and CD31. Conclusions: The histological and cytomorphological appearance of the tumou r well as the immunohistochemical findings suggest the diagnosis of maligna nt myoepithelioma, possibly derived from minor vestibulary glands or ectopi c breast tissue. Differential diagnoses are, in particular, extrarenal rhab doid tumour and 'proximal type' epithelioid sarcoma. Differentiation is imp ortant, because the tumours show a different behaviour and prognosis.