Malignant melanoma of the vulva in a nationwide, 25-year study of 219 Swedish females: clinical observations and histopathologic features.

BACKGROUND: Because the clinical and histopathologic features of vulvar melanoma had not been characterized completely in a large, homogeneous population, the authors retrospectively analyzed all such patients recorded in Sweden during a 25-year period.

METHODS: The Swedish National Cancer Registry opened its records to the authors for review of all 219 females with primary vulvar melanoma reported from 1960 to 1984. Histopathologic specimens and clinical histories of the 198 patients who qualified for this study were reanalyzed and the tumors rigorously subtyped.

RESULTS: Macroscopically amelanotic tumors were observed in 27% of patients, predominantly in glabrous skin; the clitoral area and labia majora were the most common primary sites. Of all melanomas, 46% emerged in glabrous skin, 12% emerged in hairy skin, and 35% extended to both areas. On average, approximately 2.5 times more melanomas appeared in the vulva than on the whole body surface. Overall, 57% were of the mucosal lentiginous (MLM) type, 22% were nodular melanomas (NMs), 12% were unclassified, and only 4% were superficial spreading melanomas (SSMs); this was the reverse of the order observed for cutaneous melanoma. Almost all vulvar melanomas underwent a vertical growth phase; other common features were marked thickness and ulceration, particularly in the glabrous skin. Preexisting nevi occurred in 11 cases, all in hairy skin, and 71% in conjunction with SSM but only 4% with MLM.

CONCLUSIONS: Several clinical and histopathologic features indicated that the natural history of vulvar melanomas is at variance with that of cutaneous melanomas. Because preexisting nevi, which are often considered a precursor to melanoma, were significantly linked to SSM and only in the vulvar hairy skin, melanomas in the glabrous skin apparently emerged de novo.