Risk factors for breast cancer in Tianjin, People's Republic of China.

Four hundred fifteen patients with breast cancer who were between 25 and 59 years old were interviewed. They were identified through a breast cancer screening program conducted by the Tianjin Cancer Institute during 1977-80. Controls were women who participated in the screening program but were free of breast cancer. The study confirmed early menarche, late age at first birth, and late menopause as major risk factors for breast cancer. Total duration of lactation was significantly associated with a reduction in its risk among parous women, but this was explained by higher parity among controls. No significant differences were observed between patients and controls in the amount of exposure to chest radiographs or use of hormones.