APOBEC3B and cancer: In agreement with observation in cancer cell lines, both the APOBEC3B and APOBEC3C genes show higher expression levels in ER− cancers (P < 2.2 × 10−16 and P < 3.1 × 10−5, respectively, two-sided Wilcoxon rank sum test) relative to ER+ cancers (Fig. 1b).