C-B3-01: Variation in Seven Obesity-Related Genes and Risk of Postmenopausal Breast Cancer

Abstract

Background/Aims: Obesity has been consistently associated with postmenopausal breast cancer risk. Proteins secreted by adipose tissue or involved in regulating obesity may play a role in breast tumor development. We conducted a nested case- control study among white, postmenopausal women from the American Cancer Society Cancer Prevention Study II (CPS -II) Nutrition Cohort to determine whether genes associated with obesity increase risk of breast cancer. Methods: Tagging single nucleotide polymorphisms (tagSNPs) were selected to capture common variation across seven candidate genes that encode adipose- related proteins: ADRB2, ADRB3, GHRL, HSD11B1, IRS1, IRS2, SHC1. Thirty-nine SNPs were genotyped in 648 cases and 659 controls. Logistic regression models and haplotype analysis were used to examine the association between each tagSNP and risk of breast cancer while adjusting for matching factors and potential confounders. We also examined whether these SNPs were associated with measures of adult adiposity. Results: Two of five tagSNPs in HSD11B1 were associated with breast cancer (rs11807619, P=0.006; rs932335, P=0.0002). The rs932335 C allele was associated with a nearly two-fold increased risk of breast cancer (OR=1.83; 95% CI: 1.01–3.33 for C/C versus G/G). The rs11807619 and rs932335 were highly correlated (r2=0.74), and when modeled as a haplotype, only haplotypes containing the rs932335 C allele were associated with breast cancer. Three of the eleven SNPs for IRS2 were associated with breast cancer (rs4773082, P=0.007; rs2289046, P=0.016; rs754204, P=0.03). When these 3 SNPs were examined as a haplotype, only the haplotype that included the G allele of rs2289046 was associated with breast cancer (OR=0.74, 95% CI: 0.62–0.90 for TGC compared to CAT). IRS2 rs2289046 and rs754204 were also associated with adult weight gain. None of the other SNPs in any gene investigated were associated with breast cancer or adiposity. Conclusions: Our results suggest that these tagSNPs in HSD11B1 and IRS2 mark regions of the genome that may harbor risk alleles for breast cancer, and these associations are likely independent of adiposity.