ESR1 and breast cancer: LY6D also plays an important role in cancer; it serves as a prognostic marker for advanced prostate cancer (21) and stage I non-small cell lung carcinoma (NSCLC) (22), drug resistance-associated marker for laryngeal squamous cell carcinoma (23), long-range metastasis marker for patients with ESR1-positive breast cancer (24), and a marker of urothelial and squamous cell differentiation (25).