An orthotopic 4T1 mouse breast cancer model used in this study resembles triple-negative breast tumours (ER-, PR-, HER2-) in humans (Luo et al., 2020), and we have used 4T1 tumour cells that express a lower level of NY-ESO-1, which may be comparable to the physiological level of NY-ESO-1 expression in human cancer. Here, ERBB2 is linked to cancer.