APOBEC3B and breast cancer: However, association studies with large breast cancer cohorts have shown only weak positive or negligible associations between A3B expression levels and APOBEC signature mutation loads, and clear outliers exist including tumors with high A3B and few APOBEC signature mutations and low A3B and many APOBEC signature mutations (Buisson et al., 2019; Burns et al., 2013a; Burns et al., 2013b; Nik-Zainal et al., 2014; Roberts et al., 2013).