Extremity nevus count is an independent risk factor for basal cell carcinoma and melanoma, but not squamous cell carcinoma

Background: The presence of nevi portends an increased risk for melanoma. Objective: We sought to examine the association between extremity nevus count and the risk of melanoma and keratinocyte cancers. Methods: We evaluated prospective cohorts of 176,317 women (the Nurses' Health Study, 1986-2012 and the Nurses' Health Study 2, 1989-2013) and 32,383 men (Health Professionals Follow-up Study, 1986-2012). Information on nevus count (none, 1-5, 6-14, >= 15) on the extremity was collected at baseline. Results: There were 1704 incident cases of melanoma, 2296 incident cases of squamous cell carcinoma, and 30,457 incident cases of basal cell carcinoma, with a total of 4,655,043 person-years for melanoma and 4,267,708 person-years for keratinocyte cancers. The presence of an extremity nevus was associated with an increased risk of melanoma in all anatomic areas and increased risk of basal cell carcinoma (BCC). Individuals with >= 15 nevi had the highest risk of melanoma and BCC compared to those without any extremity nevi (melanoma hazard ratio 2.79 [95% confidence interval 2.04-3.83]; BCC HR 1.40 [95% confidence interval 1.32-1.49]). No significant association was observed for squamous cell carcinoma. Limitations: Limitations of our study included self-reported nevus count and detection bias. Conclusions: Extremity nevus count is a helpful clinical marker in risk-stratifying individuals for BCC and melanoma on all body sites.