Background: Body mass index (BMI), a known breast cancer risk factor, could influence breast risk through mechanistic pathways related to sex hormones, insulin resistance, chronic inflammation, and altered levels of adipose-derived hormones. Results from studies of the relationship between BMI and second primary breast cancer have been mixed. To explore the relationship between BMI and asynchronous contralateral breast cancer (CBC), we examined whether variants in genes related to obesity, weight, and weight change are associated with CBC risk.
Methods: Variants in 20 genes [182 single-nucleotide polymorphisms (SNP)] involved in adipose tissue metabolism, energy balance, insulin resistance, and inflammation, as well as those identified through genome-wide association studies (GWAS) of BMI and type II-diabetes were evaluated. We examined the association between variants in these genes and the risk of CBC among Caucasian participants [643 cases with CBC and 1,271 controls with unilateral breast cancer (UBC)] in the population-based Women's Environmental Cancer and Radiation Epidemiology (WECARE) Study using conditional logistic regression.
Results: After adjustment for multiple comparisons, no statistically significant associations between any variant and CBC risk were seen. Stratification by menopausal or estrogen receptor (ER) status did not alter these findings.
Conclusion: Among women with early-onset disease who survive a first breast cancer diagnosis, there was no association between variation in obesity-related genes and risk of CBC.
Impact: Genetic variants in genes related to obesity are not likely to strongly influence subsequent risk of developing a second primary breast cancer.