Breast Feeding and Breast Cancer Risk: A Case-control Study in Korea

We carried out a case-control study to investigate protective effect of lactating against breast cancer in Korea. Cases (n=108) were the newly histologically identified breast cancer between December 1997 and August 1999. Hospital-based controls were selected by frequency matching method with age ($\pm$4 age) and menopausal status from the patients at the same hospital in the plastic surgery, general surgery and opthalmology department. Interviews included information on general characteristics of subjects, disease history, family history of breast cancer, vitamin supplementation, alcohol intake, food intake, and reproductive factors as well as lactation history. Odds ratio (OR) and 95% Confidence Intervals (CI) were calculated by using unconditional logistic regression. Age distribution of case control subjects were similar. Late menarche age $\geq$ 17 in premenopausal women was related to the lower risk of breast cancer OR = 0.41, 95% CI = 0.28-0.91. Family history of breast cancer was related to the higher risk of breast cancer only in premenopausal women (OR = 2.07, 95% CI = 1.35-2.71). Higher body mass index mass index (> 30) were associated with higher risk of breast cancer in postmenopausal women. For premenopausal women, women who had lactated $\geq$ 12 months to the first child had a significantly lower risk (OR = 0.53, 95% CI = 0.24-0.97) than the women had no breast feeding experience. However, results from postmenopausal women did not show an association with decreased breast cancer risk. These findings suggest that lactation may be a protective factor of breast cancer in Korean women.