Abstract GS5-07: Weight change in postmenopausal women and breast cancer risk in the women's health initiative observational study
Authors: Chlebowski RT , Luo J , Anderson GL , Simon M , Barrington W , Reding K , Manson JE , Rohan T , Wactawki-Wende J , Lane D , Strickler H , Mossavar-Rahmani Y , Freudenheim J , Saquib ATN , Stefanick M 
Published: February 2018

Abstract
Purpose
While obesity is an established breast cancer risk factor, information about the influence of weight loss on breast cancer risk in postmenopausal women is mixed precluding generation of a strong public health message regarding potential benefits of weight loss with respect to cancer risk. Therefore, we evaluated associations between weight change and invasive breast cancer risk in postmenopausal women participating in the Women's Health Initiative (WHI) Observational Study.
Patients and Methods
Postmenopausal women (n=61,335) with no prior breast cancer and normal mammogram who were not underweight (body mass index [BMI] ≥ 18.5 kg/m2), ages 50-79 years at WHI enrollment between 1993 and 1998 at 40 US clinical centers, had body weight and height measured and BMI calculated at the clinical centers at baseline and at year 3. Weight change over 3 years was categorized as: stable (no change ≤ 5%), loss (change ≥ 5%), or gain (change ≥ 5%) with weight lost intentionality determined by self-report response to direct query at year 3. Breast cancers were initially ascertained through annual survey and were centrally confirmed by medical record review. Multi-variable Cox proportional hazards regression models incorporating breast cancer risk factors and baseline BMI were used to evaluate relationships between weight change and breast cancer incidence.
Results
During 11.4 years (mean) of follow-up, 3,061 women developed invasive breast cancer. In multi-variable analyses, compared with women with stable weight (n=41,139), women with weight loss (≥ 5%) (n=8,175) had a significantly lower breast cancer risk (hazard ratio [HR] 0.88 95% confidence interval [CI] 0.78-0.98). Adjustment for mammography did not alter findings (HR 0.88 95% CI 0.78-0.99). There was no significant interaction for breast cancer effect by weight loss intentionality. Women with weight loss ≥ 15% had even lower breast cancer risk (HR 0.63 95% CI 0.45-0.90). While weight gain (≥ 5%) (n=12,021) was not associated with higher overall breast cancer risk, women with weight gain had a significantly higher risk of triple negative breast cancer (HR 1.54 95% CI 1.16-2.05). Weight change association with breast cancer incidence was examined in four subgroups: by tumor subtype (hormone receptor and HER2 status based), baseline BMI (normal, overweight, obese), race/ethnicity, and age group (50, -&lt;70 years). Effects in all subgroups was similar with no evidence of heterogeneity as no interaction term test in these analyses was significant.
Conclusion
Weight loss in postmenopausal women is associated with lower breast cancer risk. These findings suggest that postmenopausal women who lose weight may reduce their breast cancer risk.
Citation Format: Chlebowski RT, Luo J, Anderson GL, Simon M, Barrington W, Reding K, Manson JE, Rohan T, Wactawki-Wende J, Lane D, Strickler H, Mossavar-Rahmani Y, Freudenheim J, Saquib ATN, Stefanick M. Weight change in postmenopausal women and breast cancer risk in the women's health initiative observational study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS5-07.