Since we observed evidence of RR in both Tamoxifen-resistant and ESR1 mutant BC models, our findings have broad implications in both pre-menopausal women (who are commonly treated with tamoxifen) and post-menopausal women (who are commonly treated with aromatase inhibitors, which create an estrogen-depleted environment and exert selective pressure for the evolution of ESR1 mutations)4. The gene discussed is ESR1; the disease is breast cancer.