Combination Followed by Maintenance Chemotherapy Versus CDK4/6 Inhibitor Combined With Endocrine Therapy for HR Low/HER2-negative Advanced Breast Cancer: a Prospective, Randomized, Open-label Phase Ⅱ Clinical Trial

This trial is comparing two treatment strategies for advanced breast cancer that has low levels of hormone receptors (HR-low) and is HER2-negative: chemotherapy (given in combination and then as maintenance) versus a CDK4/6 inhibitor drug combined with hormone therapy — to find out which approach works better for this hard-to-treat subgroup. **You may be eligible if...** - You are 18 or older with metastatic breast cancer confirmed by biopsy - Your tumor is HER2-negative and has low hormone receptor (estrogen receptor) expression of 1-50% - You have at least one measurable lesion on imaging - You have not yet had chemotherapy for your metastatic disease **You may NOT be eligible if...** - Your tumor is HER2-positive or has no hormone receptor expression at all (unless certain criteria are met) - You have had prior chemotherapy for metastatic (stage IV) disease - You have significant heart, liver, or kidney problems - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.