Clinical Study of SHR-A1811 With or Without Letrozole in Neoadjuvant Therapy for Early-Stage HR-Positive, HER2-Low Breast Cancer

This is a prospective, randomized, multi-cohort, Phase II clinical trial. The study plans to enroll 120 patients with early-stage or locally advanced, HR-positive, HER2-low breast cancer. The primary objective is to evaluate the efficacy and safety of SHR-A1811 with or without endocrine therapy compared to standard chemotherapy as neoadjuvant treatment.

Eligible subjects will be randomized centrally via an Interactive Web Response System (IWRS) using a block randomization method. Participants will be assigned in a 1:1:1 ratio to one of three treatment cohorts:

Cohort A: SHR-A1811 plus endocrine therapy (letrozole ± ovarian function suppression \[OFS\]) Cohort B: SHR-A1811 monotherapy Cohort C: Standard chemotherapy (investigator's choice of A/EC-T or TEC regimen)

Neoadjuvant Treatment:

Subjects in Cohorts A and B will receive 8 cycles of their assigned regimen. Subjects in Cohort C will receive standard chemotherapy as per the chosen protocol.

Treatment will continue until completion of the regimen, occurrence of unacceptable toxicity, withdrawal of consent, or discontinuation at the investigator's discretion.

Assessments:

Tumor imaging for efficacy evaluation will be performed every 2 cycles, with responses assessed according to RECIST v1.1 criteria. Subjects who complete neoadjuvant treatment and are deemed eligible for surgery will undergo surgical intervention within 4 weeks after treatment completion. Pathological response will be assessed from the surgical specimen. Both radiological and pathological evaluations will be based on the assessments conducted at the study site.

Adjuvant Therapy:

Following surgery, all subjects will receive standard adjuvant endocrine therapy as clinically indicated.