Menstrual factors and cancer risk among Korean women.

BACKGROUND It has been suggested that lifetime exposure to female hormones is related to cancer risk in women. The authors investigated the association between age at menarche and menopause and cancer risk in a prospective study of Korean women. METHODS A total of 443 909 women, in the age group of 30-80 years in the 1993-94 time period were included in the analysis. During 12 years of follow-up, 17 959 incident cancer cases were identified by record linkage to the Central Cancer Registry database. RESULTS Early age at menarche was associated with an increased risk of breast cancer and a decreased risk of stomach and gallbladder cancer. Later age at menopause was associated with an increased risk of breast cancer. When the analysis was restricted to post-menopausal women, the associations of age at menarche and menopause with cancers of the breast, stomach and gallbladder persisted. CONCLUSION These findings suggest that female hormonal factors play a significant role in the development of cancer in Korean women.