Treatment of the MCF10A non-tumorigenic breast epithelial cell line with nine DNA-damaging or anti-metabolite drugs followed by measurement of the ssDNA damage marker pS4/8 RPA identified a relationship between those that induced the highest levels of both APOBEC3B and RPA phosphorylation, although this was not entirely reproduced in the estrogen-receptor-positive MCF7 breast cancer cell line. The gene discussed is APOBEC3B; the disease is breast cancer.