In multivariate Cox regression analysis, together with current prognostic markers such age, tumor size, and grade, steroid hormone receptors and APOBEC3B mRNA expression remained significant in ER + breast cancer in the analysis of DFS (HR = 1.32, 95 % CI = 1.02–1.69, P = .034, Table 2), MFS (HR = 1.43, 95 % CI = 1.07–1.91, P = .015, Supplementary Table S2), and OS (HR = 1.44, 95 % CI = 1.06–1.96, P = .02, Supplementary Table S3). Here, APOBEC3B is linked to breast carcinoma.