A 24-year-old drug addict, HIV-negative woman with a 9-month history of nodular pulmonary infiltrates with a clinical diagnosis of possible granulomatosis. She presented 1 month ago with fever and abdominal pain due to a right adnexal mass. On examination, a 12 cm right ovarian mass was seen, together with another 2 cm mass in the middle of the transverse colon, which was removed. At the same time, the patient reported a 4 cm tumour on the right thigh, located deep in the subcutaneous cellular tissue.
The ovarian tumour and the mesenteric nodule had a lobulated external surface, the section surface of which showed solid and cystic areas. In the ovary, the cells were predominantly epithelioid in morphology with prominent nucleolus and diffuse growth pattern with small cystic spaces or pseudofollicles. In the mesenteric nodule a spindle cell morphology predominated. Alternating hypercellular and hypocellular areas were observed. There were extensive and frequent areas of geographic necrosis with a tendency to preserve those tumour cells surrounding the vessels resulting in a peritheliomatous pattern. At higher magnification, the spindle-shaped tumour cells showed an oval nucleus and a non-prominent nucleolus. More than 10-20 mitoses per 10 high magnification fields were observed. Immunophenotypically the tumour expressed vimentin, S-100, HMB-45 and actin. Staining for S-100 was intense and diffuse. The tumour did not express epithelial markers or other markers such as CD 117, CD 68, CD 99, collagen IV, oestrogen receptors, progesterone receptors and inhibin. The thigh tumour subsequently removed was unrelated to the epidermis and histologically superimposable to the ovarian tumour. The distribution of the tumour nodules, the combination of histological patterns and the immunohistochemical profile was consistent with the diagnosis of metastatic malignant melanoma, originating from a primary tumour of unknown origin as the patient was scanned and no worrisome pigmented lesions were found and there was no evidence of regression of one of them.

Treatment with chemotherapy (Cisplatin, Interleukin II, Dacarbazine and Interferon alfa) was started and 3 months later, the patient died developing multiple abdominal metastases, including a 13 cm contralateral ovarian mass, retroperitoneal adenopathies and multiple subcutaneous metastases.