Epidemiology of familial predisposition for breast cancer in Japan.

The physical and reproductive traits known to be risk factors for breast cancer were correlated with familial predisposition for this disease by the use of hospital records of 3,867 patients with breast cancer, of whom 186 had one or more relatives with breast cancer and were called "familial patients." Various characteristics in the total series of patients were compared with familial patients matched for year of birth. The mean age at menarche was significantly less in familial compared with the total series of patients, especially for premenopausal patients; however, no difference was observed in the mean age at marriage between the two groups. Familial patients were slightly taller as compared to the total series of patients, but no difference was detected in body weight between the two groups. Because age at menarche and the stature are highly correlated, they may be influenced by an underlying common hormone effect that may influence the familial nature of breast cancer.