Ovarian metastatic melanoma. A diagnostic pitfall in histopathologic examination.

Malignant melanoma metastasis to the ovary is exceptional. This observation relates the case of a 33 year-old woman who presented with a voluminous unilateral, histologically poorly differentiated, ovarian mass, and discusses the differential diagnosis. Immunohistochemical studies demonstrated strong positivity for S-100 protein, HMB-45 and vimentin. We emphasize the unpredictable clinical and biologic behavior of malignant melanomas and the necessity to perform immunohistochemical study by S-100 protein and HMB-45 in a poorly differentiated metastasis to the ovary, histologically compatible with malignant melanoma; even in the absence of intracytoplasmic pigment and clinical antecedent of cutaneous malignant melanoma.