A BRIEF ORIGINAL CONTRIBUTION History of Lactation and Breast Cancer Risk

A self-administered questionnaire was completed by 1,018 women diagnosed with breast cancerdunng 1988-1989 identified through the British Columbia Cancer Registry and by 1,025 controls selected at random from the Provincial Voters List. Parous pre-menopausal women who had never nursed (odds ratio (OR) = 13, 95 % confidence interval (Cl) 0.9-2.0) or who had lactated for 1 month or less (OR = 1.8,95 % Cl 1.3-2.5) had an increased risk of breast cancer adjusted for age and parity, compared with women who had breast-fed 2 months or longer. The nsk was particularly elevated (OR = 3.0, 95 % Cl 1.6-5.4) among women who reported having tried to nurse, but who were unsuccessful. Among women who nursed for at least 2 months, there was an indication of decreasing nsk with increasing duration of nursing. Among postmenopausal parous women, no relation between lactation history and breast cancer risk was evident. Am J Epidemiol 1993; 138:1050-6. breast neoplasms; lactation There is no consensus among the results of studies of the history or duration of lac