The joint odds ratios for the development of breast cancer while on SERM therapy for five years for these two sets of SNPs ranged from 1.00 for women homozygous for both sets of favorable, low-risk alleles, to 5.71 for women homozygous for unfavorable, high- risk alleles for both ZNF423 and CTSO. In the present study, we also evaluated their joint effect on cell proliferation in the presence of tamoxifen in LCLs carrying different combinations of ZNF423 and CTSO genotypes. Here, CTSO is linked to breast cancer.