Adjuvant tamoxifen, an essential treatment for ER+ breast cancer, has been used for >3 decades to reduce the risk of breast cancer recurrence and mortality.[38] To ensure optimal benefits, patients must take tamoxifen for at least 5 years.[39] Despite the acknowledged benefits of both reduced recurrence and increased survival rates, adherence to tamoxifen is less than ideal. This evidence concerns the gene ESR1 and breast carcinoma.