In fact, TILs and immune-related genes in HR+/HER2- BC have been associated with a poor response to therapy with aromatase inhibitors as well as lower ESR1 expression levels, which are shown to be mutually exclusive with TP53 mutations in metastatic endocrine-resistant HR+/HER2- BC [58,59,60,61,62]. The gene discussed is CYP19A1; the disease is breast cancer.