When a mimicker wears strange faces: description of an osteogenic melanoma arising within an ovarian teratoma with focus on its late peritoneal relapse.

Secondary malignancies arising within mature teratomas are a rare event, originating from malignant transformation of the tissues derived from one of the three germ cell layers. Osteogenic melanoma is exceedingly rare histologic variant of malignant melanoma, in which the melanoma is associated to an osteogenic sarcoma component. To the best of our knowledge, first case of osteogenic melanoma arising within mature ovarian teratoma in a 30-year-old woman without evidence of a primary cutaneous or visceral melanoma. The present case showed an unusual morphological and immunohistochemical pattern and was incorrectly diagnosed as undifferentiated carcinoma. After a 15 years follow-up period, the patient presented a peritoneal recurrence histologically constituted by epithelioid cells with prominent osteoid formation and with immunohistochemical expression of melanocytic markers (S100, HMB-45). Heterozygote Mutation V600E/E complex has been detected in the BRAF exon 15 sequence. The case was then interpreted as osteogenic melanoma. The present case contributes to widen the spectrum of neoplasms derived from malignant transformation of ovarian teratomas and provides also new insights about the clinical behavior of osteogenic melanoma when arising outside its usual anatomical location.