Adult Overweight and Survival from Breast and Colorectal Cancer in Swedish Women.

Background: The impact of overweight duration and intensity during adulthood on the prognosis after a cancer diagnosis remains largely unknown. We investigated this association in Swedish women with breast and colorectal cancer.

Methods: A cohort of 47,051 women from the Swedish Lifestyle and Health Study was included, of whom 1,241 developed postmenopausal breast (mean age at diagnosis, 57.5 years) and 259 colorectal (mean age at diagnosis, 59.1 years) cancer. Trajectories of body mass index (BMI) between ages 20 and 50 years were estimated for the full cohort using a quadratic growth model and studied in relation to risk of death from any cause using multivariate Cox regression models among cancer survivors.

Results: Compared with patients with cancer who were never overweight (BMI < 25) during early adulthood (ages 20-50 years), the risk of early death from breast cancer increased by 3% [hazard ratio (HR) = 1.03; 95% confidence interval (CI), 1.01-1.05] and from colorectal cancer by 4% (HR = 1.04; 95% CI, 1.01-1.06) for every year lived with overweight. A higher intensity of overweight (i.e., a combination of duration and degree of overweight-a concept comparable to pack-years of cigarette smoking) further increased the risk of dying in this population. Although risks were slightly more pronounced for women diagnosed with late-stage breast cancer, no clear association was found for colorectal cancer.

Conclusions: Our results suggest that adulthood overweight duration and intensity have a long-lasting influence on breast and colorectal cancer survival.

Impact: Our study highlights the need for effective prevention of overweight and obesity starting at an early age.