Asymmetric lateral distribution of melanoma and Merkel cell carcinoma in the United States

BackgroundA recent report suggested a trend toward more ultraviolet-linked skin cancers arising on the left rather than the right side of the body in the United States.ObjectiveWe sought to test whether the reported incidences of two ultraviolet-linked skin cancers, malignant melanoma (MM) and Merkel cell carcinoma (MCC), are statistically significantly greater on the left than the right in the United States.MethodsMMs (n = 82,587) and MCCs (n = 2384) occurring on the left or right side of the face, arm, or leg that were reported in the Surveillance, Epidemiology, and End Results registry between 1986 and 2006 were included for analysis.ResultsMM and MCC were significantly more likely to present on the left than the right (P < .01 for both MM and MCC). In all, 53% of arm melanomas, 51% of facial melanomas, and 52% of leg melanomas presented on the left. A total of 55% of arm MCCs and 52% of facial MCCs presented on the left, whereas leg MCCs were equally distributed.LimitationsNational registry data did not provide information regarding sun exposure or driving habits. No equivalent registry data were available for basal or squamous cell carcinoma.ConclusionsBoth melanoma and MCC are significantly more likely to arise on the left than the right, and this effect was most prominent on the arm. Driver-side automobile ultraviolet exposure (approximately 5-fold stronger on the left than right arm) is a likely contributing factor. It may be prudent to remind individuals prone to skin cancer to take appropriate sun precautions when driving in an automobile.