<h4>Introduction</h4>The APOBEC3 family of cytidine deaminases induces somatic mutations that are highly prevalent in cancers, but the functional consequences remain largely unknown.<h4>Methods</h4>To determine these consequences, we exposed MCF7 tumorigenic breast epithelial cells to APOBEC3A, APOBEC3B or APOBEC3H Haplotype I.<h4>Results</h4>Comparative analysis between cells pre and post -APOBEC3 exposure revealed fewer deamination-dependent γH2AX foci post-APOBEC3 exposure, despite maintaining APOBEC3 protein expression. The gene discussed is APOBEC3B; the disease is cancer.