**Study Overview:** This study tests a new treatment called *iza-bren* against regular chemotherapy for a type of breast cancer called triple-negative breast cancer (TNBC) or estrogen receptor (ER)-low, HER2-negative breast cancer. TNBC is a kind of cancer that doesn't have the usual three receptors (ER, PR, and HER2) that some other breast cancers have. The study is for people whose cancer has spread or come back and can't be removed by surgery. They also can't take certain other cancer drugs (anti-PD(L)1 drugs). **Treatment Details:** *Iza-bren* is an antibody-drug conjugate, which means it’s a mix of an antibody (a protein that can attach to cancer cells) and a topoisomerase inhibitor (a drug that helps stop cancer cells from dividing). The study wants to see if *iza-bren* works better than the usual chemotherapy drugs like paclitaxel, nab-paclitaxel, carboplatin plus gemcitabine, and capecitabine. **Key Points:** - The study aims to compare *iza-bren* to regular chemotherapy. - Participants shouldn’t have had any prior systemic therapy for this cancer setting. - You may not qualify if your cancer can be treated with anti-PD(L)1 drugs or endocrine therapy.