APOBEC3B and breast cancer: In the presence of a deaminase, initiating and or paused sites would become accessible for mutation, thus it is intriguing to observe promoter proximal enrichment of mutations at TpC dinucleotides in PD4120a, a breast cancer genome with dramatic accumulation of kataegis that betrays its mutagenesis by APOBEC3B (Nik-Zainal et al., 2012).