The heterozygous CA genotype of KCNK9 rs2468677 (C/A) had increased breast cancer risk compared with the major AA genotype; however, it was found to be statistically significant only in model 2 with an additional adjustment for BMI (HR, 1.35; 95% CI, 1.00–1.80). Here, KCNK9 is linked to breast cancer.