Little is understood about the mechanism of APOBEC3 activation in cancer, except that a few signalling pathways (e.g. NF-κB and Protein Kinase C (PKC) (52)) and driver events (e.g. ERBB2 amplification, PTEN loss (53)) have been suggested to be associated with A3B expression and/or the APOBEC3 mutational signatures. Here, PTEN is linked to cancer.