Primary malignant melanoma of the ovary: a report of 9 definite or probable cases with emphasis on their morphologic diversity and mimicry of other primary and secondary ovarian neoplasms.

Most malignant melanomas encountered in the ovary are metastatic, and the recent literature has focused on such neoplasms. Primary tumors are rare with most reports being only of single cases. When the tumor is associated with teratomatous elements from which it arises, not only is the diagnosis of melanoma much more likely to be made but also is a primary nature proven. However, although all the primary tumors likely are of teratomatous origin, evidence of such an origin may be effaced resulting in problems both in identifying the tumor as melanoma and in determining if it is primary or not. In this report, we describe 9 primary or probably primary ovarian melanomas and explore the varied problems the cases posed. The patients ranged from 18 to 72 years. The tumors, all of which were unilateral, ranged from 4 to 23 cm; only 2 were black. In 6 cases, there was an associated dermoid cyst or monodermal teratoma (struma ovarii), 5 in the ipsilateral and 1 in the contralateral ovary. The tumors were variously composed of large epithelioid cells with eosinophilic cytoplasm, small cells, spindle-shaped cells, or a combination, and in 5 cases, melanin pigment (Masson Fontana positive) was identified. In all cases, most of the tumor cells had prominent nucleoli. All neoplasms had a predominantly diffuse growth pattern with a focal nested architecture in 3 cases. Other noteworthy morphological features were tumor giant cells with wreath-like nuclei (4 cases), signet ring cells (1 case), clear cells (1 case), intranuclear pseudoinclusions (2 cases), a focally myxoid stroma (2 cases), a pseudopapillary appearance caused by degeneration (2 cases), and follicle-like structures (3 cases). In 1 case in a 21-year-old, there was associated hypercalcemia, and focally, the neoplasm, which contained follicle-like structures, resembled small cell carcinoma of the hypercalcemic type. All cases tested by immunohistochemistry were positive with 1 or more melanocytic markers, and electron microscopy performed in 3 cases revealed intracytoplasmic melanosomes or premelanosomes. The wide differential potentially includes neoplasms within most of the categories of primary ovarian neoplasia, as well as metastatic melanoma, and is facilitated by thorough sampling to identify teratomatous elements, by awareness of the spectrum of melanoma in the ovary, and by positivity with melanocytic markers. This is an area where electron microscopy can still also contribute useful information.