Characterization of nonacral melanoma patients without typical risk factors.

A divergent pathway model to cutaneous melanoma is commonly accepted: sun sensitivity/chronic sun exposure and melanocytic instability. Although this dual model explains the development of most melanomas, clinical experience suggests other possible routes. The aim of this study was to explore the characteristics of patients who do not fit with these two pathways. We selected 818 patients with nonacral cutaneous melanoma and defined three groups: nevus-prone individuals, sun-sensitive individuals, and non-nevus-prone and non-sun-sensitive individuals. This group included patients without identifiable melanoma risk factors and comprised 52 patients (5.5% of the overall nonacral melanoma population). These patients were more frequently women, were more likely to present melanoma at a very young age (13.5% before 25 years), to have less frequent personal history of melanoma and remnants of pre-existing nevi, and to present tumors on the trunk and legs. We have identified a group of patients with fewer risk factors for melanoma that needs further studies to increase our understanding of melanoma development.