Lactation and Menstrual Function as Related to Cancer of the Breast

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Abstract
Inter- view data were obtained for breast cancer cases and controls admitted to Roswell Park Memorial Institute from April 17, 1955, to December 1, 1959. The age-adjusted risk of breast cancer for women who had artificial menopause or who nursed longer than 36 months was less, while risk for those who never married, were never pregnant, or who never nursed was greater than in the general female population. In more refined analyses, cases and controls were matched on age, race, religion, marital status, parity or months pregnant, and native-foreign birth. With high significance (P< .002), risk of breast cancer was found to increase at a 4.9% faster rate during menstrual years than during post-menopausal years. For lactation up to 17 months, risk increased faster than during menstrual phases. But beyond 17 months of lactation, risk accumulated significantly less rapidly than during menstrual phases. These results were applied to obtain a predicted 5.3 to 1 ratio of breast cancer incidence in the United States versus Japan. The actually reported ratio was 5.5 to 1. Further testing of the results is planned in a community study of Buffalo and Kenmore, New York.