Finding the Association between BMI and Risk of Subsequent Primary Cancer of the Breast, Lung, Colon, and Endometrium among Breast Cancer Survivors

Abstract

IntroductionThere is a large population of breast cancer survivors at risk of developing second primary cancers. Most previous studies of second cancers have utilized data from cancer registries or medical records, with limited data on potential risk factors. We examined the association between body mass index (BMI) and risk of subsequent primary cancer of the breast, lung, colon, and endometrium after first primary breast cancer. Methods A population-based case-cohort study of women aged 20-74 diagnosed with a primary invasive breast cancer between 1986-2017 was conducted in Seattle, Washington. It consisted of 760 non-cases, 430 cases diagnosed with a second primary lung cancer, 527 cases with a second primary breast cancer, 212 cases with a second primary colon/rectum, and 250 cases with a second primary endometrial cancer. Multivariable-adjusted Cox proportional hazards regression was used to estimate hazard rations (HR) and 95% confidence intervals (CI) for the association of BMI at the time of first breast cancer diagnosis with risk of second primary cancers at four anatomic sites. Results Compared to having a BMI of 18.5-24.9 kg/m2 at the time of first primary breast cancer diagnosis, having a BMI of 25-29.9 kg/m2 was associated with increased risk of second primary breast cancer (HR: 1.5; 95% CI: 1.2,1.9) and having a BMI 30 kg/m2 was associated with increased risks of second primary endometrial and breast cancers (HR: 2.3; 95% CI: 1.7,3.2 and HR: 1.5; 95% CI: 1.2,1.9, respectively). BMI was not related to risks of second primary colorectal or lung cancers. Conclusion Our findings suggest that BMI may be positively associated with associated with certain forms of second primary cancers after first primary breast cancer and that women who are overweight or obese should be more closely monitored for development of certain second primary cancers.