ERBB2 and breast cancer: Cluster 5 (n = 62) was enriched for the APOBEC-1, APOBEC-2, Intra-Chr, and L-Intra-Chr signatures, and was also enriched for HER2-positive tumours, relating Her2-amplification and APOBEC deamination processes for approximately 11% of breast cancers, as previously reported [29].