Using HapMap data, we selected four putative functional tag SNPs in APEX1 (rs1130409 and rs3136817) and OGG1 (rs1052133 and rs2072668) and further evaluated the genetic interactions of these four polymorphisms and their relation to breast cancer risk among the study population of Han women living in the Gansu area in Northwest China. Here, APEX1 is linked to breast cancer.