Primary malignant melanoma of the vulva--an aggressive tumor for modeling the genesis of non-UV light-associated melanomas.

Malignant melanomas appear in such sun-shielded areas as the vulva, challenging conventional knowledge that they are associated with UV radiation. Based on 1442 patients with vulvar melanomas the tumors' epidemiology, clinical manifestations, histopathology, molecular genetics, treatment strategies, and prognosis were surveyed. Despite their sun-shielded location and rare incidence, vulvar melanomas were, on average, more dense than melanomas on the body surface and nearly the density of melanomas in chronically sun-exposed skin of the head and neck. Vulvar melanomas differed markedly from cutaneous melanomas, as evidenced by histopathological lesions and molecular genetics. Most melanomas were located on the glabrous skin as opposed to the hairy skin within the vulva and differed significantly in biological properties. The prognosis for the patients was poor, and in the 11 largest studies of surgical strategies, none offered a significant survival advantage. Tumor thickness and ulceration were usually significant predictors of (poor) prognosis in multivariate analyses along with macroscopic amelanosis, angioinvasion or DNA non-diploidy in some reports. Clear-cut biological differences between vulvar and cutaneous melanomas and between melanomas within different vulvar sites provide new paths for extensive research on melanomagenesis and for potential therapies. Additionally, studies of vulvar and other extracutaneous melanomas should characterize subgroups of cutaneous melanomas and identify their cause(s), which are apparently not linked to UV radiation.