Risk factors for female breast cancer. A hospital-based case-control study in Madras, India.
Five hundred and thirty-one histologically confirmed breast carcinoma cases examined from 1983 to 1986 inclusive at the Cancer Institute (WIA), Madras, India, were matched for age, socioeconomic class and menopausal status with an equal number of controls. Cancer patients without diseases in breast, gynaecological organs or endocrine glands were used as controls. Risk factors for breast cancer were analyzed separately in the premenopausal and the postmenopausal groups. In neither group was there significant association between age at menarche and breast cancer risk. Single women had higher risk than married women. Nulliparity was found to be a risk factor in premenopausal women only. The relative risk increased with age at marriage and age at first birth. A three-fold risk was noted in both pre- and postmenopausal groups when the interval between age at first birth and menarche was more than 12 years and also in women who attained menopause between the age of 44-49.