A Study of SKB264 Versus Investigator's Choice of Chemotherapy in Subjects With Unresectable Locally Advanced, Relapsed, or Metastatic HR+/HER2- Breast Cancer Who Have Previously Failed Endocrine Therapy

Required: HER2 (ERBB2) negative

Required: ESR1 positive

Required: PR (PGR) positive

Must have received: endocrine therapy — locally advanced, relapsed, or metastatic

disease progression during or after the most recent treatment prior to enrollment; The investigator assessed that the patient could not continue to benefit from endocrine therapy

Cannot have received: systemic chemotherapy

Exception: adjuvant/neoadjuvant chemotherapy allowed if progression >6 months after completion

No prior systemic chemotherapy for locally advanced, relapsed, or metastatic stages. Subjects who previously received adjuvant/neoadjuvant chemotherapy and progressed >6 months after completion of the last chemotherapy treatment will be allowed

Cannot have received: TROP2-targeted therapy

Prior TROP2-targeted therapy

Cannot have received: topoisomerase I inhibitor (including antibody-drug conjugates)

any treatment containing chemotherapeutic agents targeting topoisomerase I (including antibody-drug conjugates [ADCs])