ESR1 and cancer: Prior studies of ER+/HER2− disease suggest that AI has an immune-modulating effect, leading to an enrichment of tumour-infiltrating cells and immune-related characteristics, as well as emphasizing the importance of tumour microenvironment in cancer progression and therapeutic responses.29, 30, 31, 32, 33 Our study extends these observations to ER+/HER2+ disease.