Influence Of Obesity On Risk Of Second Cancers Among A Cohort Of U.S. Women With Breast Cancer

Gretchen GIERACH, National Cancer Institute, National Institutes of Health, United States
CURTIS R. 1 , PFEIFFER R. 1 , MULLOOLY M. 1 , HOOVER R. 1 , NYANTE S. 2 , SPENCER FEIGELSON H. 3 , GLASS A. 4 , BERRINGTON DE GONZALEZ A. 1

1 Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
2 Department of Radiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
3 Kaiser Permanente Institute for Health Research, Denver, Colorado, USA
4 Kaiser Permanente Northwest Center for Health Research, Portland, Oregon, USA

Purpose: Increasing breast cancer incidence in the U.S., along with the aging population and improved survival, have resulted in a greater number of women at risk of developing a new malignancy.  We investigated the association of elevated body mass index(BMI)—a surrogate marker of obesity—with risk of second primary cancers among breast cancer patients in a general community health plan.  

Methods: Our retrospective cohort includes 7,541 women, ages 24-85 years, with a primary diagnosis of invasive breast cancer at Kaiser Permanente Northwest or Colorado between 1990 and 2008 and who survived for ≥one year.  We assessed second cancer risk associated with BMI, calculated based on the patient’s height and weight from electronic medical records.  Relative risks(RRs) and 95% confidence intervals(CIs) were estimated using Poisson regression adjusting for study site, age and stage at diagnosis, ER status of initial tumor, time since initial breast cancer, diagnosis year, and breast cancer treatments (tamoxifen, aromatase inhibitors, chemotherapy with an alkylating agent, radiotherapy). 

Results:  Over a median(range) of 6.3(1.0-20.9) years of follow-up, 11.2% of breast cancer patients were diagnosed with a second primary cancer (including 248 contralateral breast, 83 colorectal, and 62 endometrial cancers).  Obese women(BMI:30+ kg/m2) experienced significantly increased risks of contralateral breast (RR=1.51, 95%CI:1.09-2.13) and endometrial (RR=2.56, 95%CI:1.27-5.59), but not colorectal (RR=1.04, 95%CI:0.58-1.89), second primary cancers as compared with normal weight women(BMI:18.5-<25 kg/m2).  For each 5 kg/m2 increase in BMI, we observed significantly increased risks of contralateral breast (RR=1.18, 95%CI:1.07-1.29) and endometrial (RR=1.40, 95%CI:1.19-1.64) cancers, respectively.

Conclusions:  Our results suggest that higher BMI, a modifiable risk factor, significantly increases risk of contralateral breast and endometrial cancers following a first breast cancer diagnosis.  Reducing obesity may represent an effective strategy for second cancer risk reduction among breast cancer patients, but this hypothesis requires confirmation in clinical trials.

Funding source: NCI Intramural Research Program, NIH