Breast cancer in men: aspects of familial aggregation.

Familial aggregation of breast cancer in males was investigated in a population-based case-control study. Cases were ascertained from 10 Surveillance, Epidemiology, and End Results Program registries in the United States between 1983 and 1986. Controls were identified by random-digit dialing and from lists of Medicare recipients. The relative odds of developing breast cancer were similar in men with affected paternal and maternal relatives and in men with affected mothers and sisters. The risk increased with the number of affected relatives. The relative odds of developing breast cancer were greater in men with first-degree relatives who developed their mammary neoplasm before the age of 45 than in men with older first-degree affected relatives; the enhancement of risk in men with an affected sister was greater in those under age 60 than in older men. These results are similar to those observed by others in studies of breast cancer in women.