Interestingly, the significantly positive correlation between the number of C>T/G>A mutations per tumor exome and APOBEC3B mRNA levels is observed in ER+ cancers (ρ = 0.32, P = 7.09 × 10−15), but not in ER− cancers (ρ = 0.04, P = 0.60, Fig. 4a). This evidence concerns the gene APOBEC3B and cancer.