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The association between weight, BMI and breast cancer was analyzed on 94,805 women of the E3N cohort according to their menopausal status. Seven hundred eighty-six incident invasive premenopausal breast cancers and 1,522 incident invasive postmenopausal breast cancers occurred during a mean follow-up of 9.7 years. Weight and BMI were updated every 24 months and considered as time-dependent variables. Data were analyzed using multivariate Cox proportional hazards models. Trend RRs of premenopausal breast cancer were 0.97 (0.92-1.01) for a 5 kg increase in weight and 0.96 (0.91-1.01) for a 2 kg/m(2) increase in BMI, adjusted for other known risk factors. Opposite trend RRs were found after menopause: 1.05 (1.02-1.08) for weight and 1.06 (1.02-1.09) for BMI, respectively, for similar increases. Women with a BMI of over 30 kg/m(2) had a RR of premenopausal breast cancer of 0.66 (0.40-1.10) compared to those with a BMI of between 18.5 and 25 kg/m(2). Postmenopausal women with a BMI of over 30 kg/m(2) had a RR of breast cancer of 1.23 (1.00-1.59). The increase in risk of postmenopausal breast cancer with increased weight or BMI was similar whatever the HRT used, although the point estimates were higher in HRT users. We strongly recommend to use anthropometric measurements updated during follow-up to assess the effect of weight, BMI on breast cancer risk.

Recent reviews reach conflicting conclusions on breast cancer risk after spontaneous or induced abortion. E3N is a large-scale cohort study collecting detailed information on environmental and reproductive factors. We investigated the relation between breast cancer and a history of induced and/or spontaneous abortion, using the data from the 100,000 women aged 40-65 at entrance in 1990. Among them, over 2,600 new invasive breast cancers had been diagnosed by June 2000. Multivariate analysis, adjusted for known potential confounders, showed no association between a history of induced abortion and breast cancer risk either in the whole population (relative risk [RR] = 0.91, 95% confidence interval [CI] 0.82-0.99) or in subgroups defined by parity or by menopausal status. Overall, the association between spontaneous abortion and breast cancer was not significant (RR = 1.05, 95% CI 0.95-1.15). However, there is a suggestion of increased risk with increased number of miscarriages (RR = 1.20, 95% CI 0.92-1.56 after 3 or more). Moreover, an interaction with menopausal status was observed. In premenopause, the risk decreased with increasing number of spontaneous abortions, whereas it increased in postmenopause. Among nulliparous and parous women, the relative risk estimates were respectively equal to 1.16 (95% CI 1.04-1.30, p trend < 0.0008) and 1.14 (95% CI 1.01-1.28, p trend = 0.005). Premenopausal breast cancer, on the other hand, appeared to be less frequent in women who had had repeated miscarriages. We conclude that there is no relationship between breast cancer and induced abortion but that an association with spontaneous abortion is possible and may depend on menopausal status.