This study is for people with a type of breast cancer called *triple negative breast cancer* that has spread to other parts of the body. It is called "triple negative" because the cancer cells don't have the typical three receptors (proteins) found in most breast cancers. **PD-L1 positive** means that the cancer cells have a certain protein that affects the immune system. The study tests if high dose radiation therapy, a treatment that uses strong x-rays to kill cancer cells, works well when combined with **pembrolizumab**, a medicine that helps the immune system fight cancer, and with chemotherapy drugs like paclitaxel, nab-paclitaxel, carboplatin, and gemcitabine. These drugs can stop cancer cells from growing. Participants will receive radiation therapy and medication in cycles, repeating every 21 to 28 days. The study is looking at how these treatments together can help fight cancer. **Key Points:** - The study involves cycles of treatment every 21-28 days. - Patients must have metastatic triple negative breast cancer. - The study will check the cancer's response to the treatment and may have some risks. Patients will have check-ups every 12 weeks after the study treatment is completed.