Tamoxifen therapy has been the mainstay of endocrine therapy for both early and advanced ER+ breast cancer patients.26 However, the effectiveness of tamoxifen treatment is limited due to drug resistance, and consequently patients are refractory to the tamoxifen treatment, which presents a significant clinical hurdle.1 It spurs the development of novel theranostic approaches to early diagnosing and effectively treating breast cancer. The gene discussed is ESR1; the disease is breast cancer.