This prospective, response-adapted phase II study evaluates the efficacy and safety of neoadjuvant culmerciclib in combination with aromatase inhibitors in patients with highly proliferative ER-positive/HER2-negative breast cancer. All patients initially receive induction treatment with culmerciclib plus endocrine therapy, followed by on-treatment assessment of biological and clinical response. Patients demonstrating an adequate response continue the same regimen, whereas those with a suboptimal response are transitioned to alternative treatment strategies prior to surgery. This adaptive approach aims to optimize treatment selection, improve therapeutic efficacy, and avoid unnecessary exposure to ineffective therapy.
Absolute neutrophil count ≥1.5 × 10⁹/L (without growth factor support within 14 days);
Platelet count ≥100 × 10⁹/L (without transfusion or supportive therapy within 7 days);
Hemoglobin ≥100 g/L (without transfusion within 7 days).
Total bilirubin ≤1 × upper limit of normal (ULN);
None
Sequential
Culmerciclib
DrugCDK2/4/6 inhibitor
Aromatase Inhibitors
DrugLetrozole or anastrozole
Complete cell cycle arrest (CCCA)
Ki67≤2.7%
the proportion of patients with Residual Cancer Burden (RCB) class 0-1
Total Pathological Complete Response (tpCR) Rate
Objective Response Rate (ORR)
Event-Free Survival (EFS)
EFS is defined as the time from randomization to any of the following events: precludes surgery, local or distant recurrence, second primary malignancy, or death due to any cause.
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