Abstract Malignant melanoma (MM) simultaneously involving the ovary and breast is a rare manifestation of the disease. We report a case of amelanotic MM of unknown primary origin manifesting as a large ovarian solid mass at its first clinical presentation. A 46-year-old woman presented with a two week history of lower abdominal pain. Imaging studies revealed an 18 cm right ovarian mass and a 1.1 cm left breast mass. The ovarian mass was first removed and it showed smooth capsule. Histologically, the tumor exhibited predominantly solid and nested growth patterns with scattered follicle-like spaces. The cells had large atypical nuclei with prominent nucleoli, and brisk mitotic activity. No melanin pigment was identified. No evidence of mature teratoma in the ovary was found. Immunohistochemically, the tumor was diffusely positive for SOX10, S-100, HMB-45, Melan-A and WT-1, and negative for cytokeratins, PAX-8, ER, PR, CD45, SALL4, and inhibin. Biopsy of the breast lesion showed a poorly differentiated malignancy with identical morphology. A diagnosis of metastatic melanoma to the ovary and breast was established. Thorough physical examination and imaging study revealed no evidence of cutaneous, uveal, or mucosal lesions. Probably, a primary MM was occult or had regressed. Subsequent molecular test for BRAF V600E mutation in the tumor was positive. The patient rapidly developed widespread metastasis. Immunotherapy was initiated; she had excellent response with significant tumor regression at her six month follow up visit. This case represents an example that making correct and timely diagnosis of metastatic melanoma followed by prompt targeted therapy significantly improved the patient’s clinical outcome.
Keywords: metastatic melanoma; ovary; breast; BRAF V600E mutation