Risk of breast cancer in young women in relation to body size and weight gain in adolescence and early adulthood

Findings have been inconsistent on effects of adolescent body size and adul t weight gain on risk of breast cancer in young women. These relations were examined in a population-based case control study of 1590 women less than 45 years of age newly diagnosed with breast cancer during 1990-1992 in thre e areas of the US and an age-matched control group of 1390 women. Height an d weight were measured at interview and participants asked to recall inform ation about earlier body size. Logistic regression was used to estimate the relative risk of breast cancer adjusted for other risk factors. Women who were either much heavier or lighter than average in adolescence or at age 2 0 were at reduced risk. Weight gain after age 20 resulted in reduced risk. but the effect was confined to early-stage and, more specifically, lower gr ade breast cancer. Neither the risk reduction nor the variation by breast c ancer stage or grade was explained by the method of cancer detection or by prior mammography history. These findings suggest that relations between br east cancer risk in young women and body weight at different ages is comple x and that the risk reduction with adult weight gain is confined to less ag gressive cancers.