Hormone Therapy

This phase II trial studies how well a vaccine, STEMVAC, works in combination with standard endocrine-based therapy (ET) with a CDK4/6 targeted drug therapy, or with the chemotherapy drug capecitabine, in treating patients with hormone receptor (HR)-positive, HER2-negative breast cancer that has spread from where it first started (primary site) to other places in the body (metastatic). STEMVAC is designed to target proteins that cancer cells use when they become more aggressive and start to spread, and it is believed to work by boosting the immune system to recognize and destroy the invader tumor cells that are causing the disease. Standard ET is treatment that adds, blocks, or removes hormones in order to slow or stop the growth of cancer. Standard CDK4/6 inhibitors, including abemaciclib, may stop the growth of tumor cells and may kill them by blocking some of the enzymes needed for cell growth. Capecitabine is in a class of medications called antimetabolites. It is taken up by tumor cells and breaks down into fluorouracil, a substance that kills tumor cells. Giving STEMVAC in combination with standard ET or chemotherapy may be an effective treatment for metastatic HR positive, HER2 negative breast cancer.

This phase II trial tests reduced post surgery (adjuvant) therapy for patients with early breast cancer who have confirmed that the disease has responded completely (pathologic complete response) after pre surgical treatment (neoadjuvant) therapy and do not have any tumor genetic material (molecular residual disease) circulating in their blood. Standard of care treatment after surgery consists of 1 year of pembrolizumab for patients with triple negative breast cancer or trastuzumab with or without pertuzumab to complete 1 year of treatment. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Pertuzumab and trastuzumab are monoclonal antibodies and forms of targeted therapy that attach to a receptor protein called HER2. HER2 is found on some cancer cells. When pertuzumab or trastuzumab attach to HER2, the signals that tell the cells to grow are blocked and the tumor cell may be marked for destruction by the body's immune system. Lowering the total amount of cancer therapy after breast surgery, may continue to keep the great tumor response to treatment, and may help lower the amount of side effects patients have.