The differential diagnosis of metastatic ovarian malignant melanoma from primary ovarian tumors is a significant challenge, particularly if there is no obvious primary site. A 39-year-old patient with bilateral ovarian malignant melanoma presented as stage IV primary ovarian tumor, with metastases in the omentum and spleen. She underwent a total abdominal hysterectomy and bilateral salpingo-oopherectomy with infracolic omentectomy and splenectomy. The diagnosis on examination of frozen sections was inconclusive. The final diagnosis was made by immunohistochemistry. The sections showed positive staining with HMB-45, vimentin, S-100, and no staining for cytoceratin, inhibin, calretinin and caldesmon. After the operation, the MRI at the 14th postoperative day revealed metastatic lesions in the vertebrae, sacrum, bilateral humerus and femur and in the cerebral cortex, together with edema and hemorrhagic foci. The patient stayed in the intensive care unit for 12 weeks until her death due to cardio-respiratory arrest. This case highlights the clinical fact that metastatic malignant melanoma may mimic primary ovarian tumor with an occult or regressed primary. Both the standard pre-operative imaging modalities (such as CT, MRI) and the histo-pathologic examination of the frozen sections may be inconclusive in the differentiation of ovarian melanoma from epithelial ovarian malignancies. The final diagnosis could be established by immunohistochemistry. Intra-abdominal debulking surgery would not prolong the survival of metastatic ovarian melanoma because of the occult or rapid metastasis to the extra abdominal sites of the tumor.

Keywords: Melanoma, ovary, metastatic melanoma, amelanotic melanoma