Toci +/- SOC Chemo for Metastatic Triple Negative and ER-positive, HER2-negative Breast Cancers

This study is testing whether adding tocilizumab — a drug that reduces inflammation — to standard chemotherapy can improve outcomes for people with triple-negative or hormone receptor-low breast cancer that has spread or cannot be treated with surgery. **You may be eligible if...** - You are 18 or older - You have locally recurrent or metastatic breast cancer that is triple-negative or has very low hormone receptor expression - You have not previously received chemotherapy for advanced/metastatic disease - You are in good enough health to receive chemotherapy **You may NOT be eligible if...** - You have already received chemotherapy for metastatic breast cancer - You have uncontrolled brain metastases - You have a history of serious infections or immune system disorders - You are pregnant or breastfeeding - You have had prior treatment with a CDK4/6 inhibitor or certain other targeted therapies - You have significant heart, liver, or blood count problems Talk to your doctor to see if this trial is right for you.