CTSO and breast cancer: Our previous case-control genome-wide association study (GWAS) performed with samples from the NSABP P-1 and P-2 breast cancer SERM chemoprevention trials identified two SNP signals that were associated with breast cancer risk, including one in which the variant SNP genotype near the CTSO gene was associated with increased risk for the development of breast cancer and a second signal for which the variant SNP genotype in the ZNF423 gene was associated with decreased risk for the development of breast cancer in women treated with tamoxifen or raloxifene [20].