A case-control study of malignant melanoma of the trunk among white males in upstate New York.

To address the increase in the incidence of cutaneous melanoma in upstate New York in recent decades, a case-control study was conducted of the constitutional and environmental risk factors for malignant melanoma of the trunk among white males. Cases were identified from the New York Cancer Registry from 1977 through 1979 (the period of the greatest relative increase in incidence), and controls were selected using random digit dialing methods. A total of 324 cases or their next-of-kin and 415 controls were interviewed regarding physical and sociodemographic characteristics, lifestyle habits, and medical histories. The following variables were statistically significant in the final logistic regression analysis: birthmarks (O.R. = 3.87); sunburn easily (O.R. = 1.83); fair skin tone (O.R. = 1.63); northern European ancestry (O.R. = 1.51); blue eye color (O.R. = 1.46); and participation in water sports (O.R. = 2.02). Interaction terms between constitutional and environmental variables resulted in a significant relationship between the presence of freckles and bathing two or more times per day. Among freckled individuals, those who bathed more than once per day had a sixfold elevation in the risk compared to those who bathed less often. In comparison, the odds ratio for frequent bathing among men without freckles was only 1.24. The data suggest the following hypothesis for further study: the possibility that frequent bathing may be deleterious, especially among freckled individuals or those with pigmented nevi.