ERBB2 and breast cancer: In breast cancer, higher TIL levels are seen in triple-negative (TNBC) and HER2 positive (HER2+) tumours, compared with ER+/HER2- tumours.12 T cells comprise the majority of the TIL population in breast cancer,13 and observations of TILs in these cancers provide insight into their immunogenicity, suggesting that TNBC and HER2+ cancers are more immunogenic than ER+/HER2− cancers.3