Background: Our recent genome-wide association study identified a novel breast cancer susceptibility locus at 9q31.2 (rs865686). Methods: To further investigate the rs865686-breast cancer association, we conducted a replication study within the Breast Cancer Association Consortium, which comprises 37 case-control studies (48,394 cases, 50,836 controls). Results: This replication study provides additional strong evidence of an inverse association between rs865686 and breast cancer risk [study-adjusted per G-allele OR, 0.90; 95% confidence interval (CI), 0.88; 0.91, P =2.01 × 10-29] among women of European ancestry. There were ethnic differences in the estimated minor (G)-allele frequency among controls [0.09, 0.30, and 0.38 among, respectively, Asians, Eastern Europeans, and other Europeans; P for heterogeneity (Phet) = 1.3 × 10-143], but no evidence of ethnic differences in per allele OR (Phet = 0.43). rs865686 was associated with estrogen receptor-positive (ER+) disease (per G-allele OR, 0.89; 95% CI, 0.86-0.91; P = 3.13 × 10-22) but less strongly, if at all, with ER-negative (ER+) disease (OR, 0.98; 95% CI, 0.94-1.02; P = 0.26; Phet = 1.16 × 10-6), with no evidence of independent heterogeneity by progesterone receptor or HER2 status. The strength of the breast cancer association decreased with increasing age at diagnosis, with case-only analysis showing a trend in the number of copies of theGallele with increasing age at diagnosis (P for linear trend = 0.0095), but only among women with ER+ tumors. Conclusions: This study is the first to show that rs865686 is a susceptibility marker for ER+ breast cancer. Impact: The findings further support the view that genetic susceptibility varies according to tumor subtype.
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