Plantar melanoma: a case-control study in Paraguay

In Paraguay, the plantar surface of the foot is the most common site for malignant melanoma, as it is in several other populations worldwide, most notably in those of African descent. Here, we report the results of the first case-control study of plantar melanoma, carried out in Paraguay. Sixty incident, histologically confirmed cases of plantar melanoma and 256 hospital controls were recruited in 11 hospitals throughout the country during 1988-93. Information was collected on general demographic, social, and lifestyle variables, on external exposures of feet (shoewear, work activities, injuries), and on some constitutional factors (skin, eye and hair color, and pigmented lesions of the feet). Few of the factors examined appeared to be associated with the risk of plantar melanoma. Adjusted for possible confounders, the strongest association was found for reported injuries (odds ratio [OR] = 40.9, 95 percent confidence interval [CI] = 14.8-112.7) and for occurrence of naevi on the soles (OR = 5.9, CI = 2.5-14.3). Walking barefoot did not seem to contribute to the risk although an outdoor workplace was associated with an increased melanoma occurrence (OR = 2.3, CI = 1.1-4.8). Future studies should be aware of problems of recall bias with respect to previous injuries, and ensure that evaluation of pigmentation of the sole is carried out blind to case/control status.