APOBEC3B and breast cancer: While it is anticipated that immune activation reflected by an increase in tumour-infiltrating immune cells would lead to reduced breast cancer risk in APOBEC3B deletion carriers, the conundrum between increased tumour-infiltrating immune cells and increased breast cancer risk in these individuals could be attributed to the increased propensity to develop higher mutation load in APOBEC3B deletion carriers [9] and this may override immune activation as previously suggested [10].