As shown in Table 1, by adjusting the marital status, educational level, occupation, and family history of cancer, we found a significant association between the hypermethylation of OPRM1 in PBL DNA and the risk of breast cancer (OR = 1.914, 95%CI = 1.357–2.777, P = 0.000). The gene discussed is OPRM1; the disease is breast cancer.