Efficacy and Safety of Ribociclib Combined With AI Versus Physician&Amp;#39;s Choice of Chemotherapy Sequential Endocrine Therapy in ER Middle-low-expression/HER2-negative Advanced Breast Cancer (Rachel)

This study (RACHEL) is testing whether ribociclib (a targeted oral cancer pill) combined with an aromatase inhibitor (a hormone-blocking drug) works better than chemotherapy followed by hormone therapy in women with a specific type of advanced breast cancer: estrogen-receptor positive (but only weakly, 10–50% expression), HER2-negative. **You may be eligible if...** - You are a woman 18 or older with advanced or metastatic breast cancer - Your tumor is estrogen-receptor positive (ER expression 10–50%) and HER2-negative - You are in reasonable overall health (ECOG 0–2) - Your cancer has been confirmed by tissue biopsy **You may NOT be eligible if...** - Your breast cancer has very high ER expression (above 50%) or is HER2-positive - You have already received multiple lines of treatment for advanced disease - You have serious organ problems or another active cancer - You are male Talk to your doctor to see if this trial is right for you.