Cancer in families of former medical students followed to midlife: prevalence in relatives of subjects with and without major cancer.

In an ongoing longitudinal study of former medical students, now physicians in midlife, the prevalence of cancer among relatives of 46 probands affected by cancer has been compared with that of two control groups of cancer-free probands. Overall, the prevalence of cancer among relatives of the three groups of probands was similar. However, male probands with cancer appeared to have a greater prevalence of cancer among their relatives than did male cancer-free probands, while the corresponding comparisons for the smaller groups of female probands showed the opposite tendency. Among the relatives of cancer probands of either sex, there was evidence of familial clustering of cancer. Where two relatives in a proband's family had the same type of cancer, the two relatives were usually on the same side (paternal or maternal) of the family. Ages at onset of cancer and types of cancer in relatives of the cancer and cancer-free probands did not reveal any significant differences.