The reasoning behind these suggestions included the following observations: A3B is overexpressed in greater than 50% of breast tumours; in more than 75% of BRCA cell lines, and it was the only detectable DNA deaminase activity in BRCA cell extracts [3,13]; increased A3B levels correspond positively with overall cytosine mutational loads [3] and A3B expression associates with worse clinical outcomes of hormone therapy resistance in BRCA [140,141]. The gene discussed is APOBEC3B; the disease is breast neoplasm.