The two major reasons for the recent significant intensification of efforts on understanding the functional importance of the APOBEC3B gene are (i) the observation that activation of APOBEC3B in cancer leads to the generation of specific hypermutation signatures in breast and other cancer genomes [55, 57, 58] and (ii) the association of the APOBEC3B gene deletion with breast cancer risk [17, 25]. Here, APOBEC3B is linked to cancer.