Resumen:
Background: Obesity is a well-known risk factor for some types of cancer including post-menopausal breast cancer. Nevertheless, the influence of adiposity over life course on cancer risk remains poorly understood. The objective of this study was to assess body shape trajectories in early and middle life in relation to subsequent risk of breast cancer in a Mediterranean cohort. Methods: We used a group-based modelling approach to assess body shape trajectories from age 5 to 40 years, among 10679 women from the SUN cohort study from 1999 to 2014. Four distinct body shape trajectories were identified (lean-heavy increase, medium-stable, medium-heavy increase and heavy-stable). Cox regression models were used to estimate the hazard ratio (HR) for breast cancer according to the assigned body shape trajectory. Results: Among 106,537 women-years of follow-up a total of 133 probable incident cases of breast cancer were identified (70 of these cases were confirmed). When compared to those in the medium-stable category, women who were lean and had a marked increase (lean-heavy increase category) showed a subsequent higher risk of probable breast cancer (HR¿=¿1.55, 95%CI 1.05-2.29). When stratifying according to menopausal status, there was a higher risk of probable postmenopausal breast cancer for women in the lean-heavy increase category (HR¿=¿2.0, 95%CI 1.06- 3.80) compared to the medium-stable group. The statistical power was reduced and significance was lost when we considered only confirmed cases.