ctDNA-Guided De-Escalation of Adjuvant Chemotherapy With Dalpiciclib in HR-Positive/HER2-Negative Breast Cancer

"Patients receive 4 cycles of neoadjuvant dalpiciclib (125 mg orally, days 1-21 of 28-day cycles) combined with an aromatase inhibitor (letrozole/anastrozole/exemestane). Post-surgery treatment is guided by ctDNA status: （1）ctDNA-negative at baseline and post-neoadjuvant, with post-op Ki67 ≤10% :Continue dalpiciclib + endocrine therapy (ET) for 2 years； （2）ctDNA-positive → negative, or persistently ctDNA-negative with post-op Ki67 \>10% :Randomized 1:1 to:~* Arm B1: Dalpiciclib + ET for 2 years.~* Arm B2: Adjuvant chemotherapy (investigator's choice) → dalpiciclib + ET for 2 years；（3）Persistently ctDNA-positive or ctDNA-negative → positive:~Mandatory adjuvant chemotherapy → dalpiciclib + ET for 2 years. Premenopausal women undergo ovarian suppression with LHRH agonists."

Patients receive 4 cycles of taxane-based neoadjuvant chemotherapy (e.g., paclitaxel 80 mg/m² weekly or docetaxel 75-100 mg/m² triweekly) before surgery. Post-surgery adjuvant chemotherapy (physician's choice) may be administered. This arm serves as the control group for comparing standard chemotherapy efficacy.