Background: Weight gain after diagnosis is common among women with breast cancer, yet results have been inconsistent among the few studies examining its effects on survival.
Methods: We examined the effects of weight gain on mortality among a cohort of 1436 women diagnosed with a first primary breast cancer in 1996–1997, on Long Island, NY. Subjects were interviewed soon after diagnosis and again after approximately 5 years. Weight was assessed at each decade of adult life; 1 year before, at, and 1 year after diagnosis; and at the time of follow-up. Mortality through the end of 2005 was assessed using the National Death Index. Proportional hazards regression was used while using a selection model to account for missing data.
Results: Compared with women who maintained their prediagnosis weight (±5%), those who gained more than 10% after diagnosis had worse survival (hazard ratio [HR] = 2.67; [95% credible interval = 1.37–5.05]). The effect was more pronounced during the first 2 years after diagnosis (>5% gain: all-cause mortality in the first 2 years, HR = 5.87 [0.89–47.8] vs. after 2 years, 1.49 [0.85–2.57]); among women overweight before diagnosis (overweight women: all-cause HR = 1.91 [0.91–3.88] vs. ideal-weight women, 1.39 [0.62–3.01]); and for women who had gained at least 3 kg in adulthood before diagnosis (≥3-kg gain before diagnosis: 1.80 [0.99–3.26 vs. <3 kg gain before diagnosis: 1.07 [0.30–3.37].
Conclusions: These results highlight the importance of weight maintenance for women after breast cancer diagnosis.