Immunotherapy medicines are relatively new and have not been studied as long as surgery, chemotherapy, radiation therapy, and hormonal therapy.
There are three immunotherapies approved by the U.S. Food and Drug Administration (FDA) to treat breast cancer: the immune targeted therapies Herceptin (chemical name: trastuzumab), Perjeta (chemical name: pertuzumab), and Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine). These three medicines treat HER2-positive breast cancer by targeting the HER2 receptors on breast cancer cells.
It’s difficult right now to say who will benefit from immunotherapies currently under investigation, such as vaccines and immune checkpoint inhibitors. Much of the research looking at immunotherapies to treat breast cancer is focusing on metastatic disease, especially triple-negative breast cancer: breast cancer that is estrogen-receptor-negative, progesterone-receptor-negative, and HER2-receptor negative. So, it seems likely that if a new immunotherapy medicine is approved to treat breast cancer it will be for metastatic triple-negative disease.
“We know that not all tumor types are the same, and also that every patient's tumor is going to be unique,” Leisha Emens, M.D., Ph. D, explained in an interview. She is associate professor of oncology at the Bloomberg-Kimmel Institute for Cancer Immunotherapy at Johns Hopkins University. Dr. Emens specializes in cancer immunotherapy. Her research focuses on the development and implementation of breast cancer immunotherapies (including vaccines and immune checkpoint inhibitors) in combination with traditional cancer treatments and other drugs that activate the immune system.
“One reason that triple-negative breast cancer is more susceptible to immune therapy is that these tumors may have more genetic mutations, referred to as mutational load,” she continued. “These mutations cause the tumor cells to produce unique antigens that look foreign to the immune system. It might be that a personalized vaccine composed of these unique antigens could work well to induce or amplify T-cells in patients with triple-negative breast cancer who do not have sufficient T-cells in the tumor immune microenvironment at diagnosis.
“We still need to learn a lot to be able to predict which patients may respond to immunotherapy,” Dr. Emens continued. “For some breast tumors, the mutational load may be important, and for others that may not be the case. Also, the presence of PD-L1 [a checkpoint protein that helps the immune system recognize cells as part of the body, rather than a foreign invader] in the tumor makes it more likely that a patient will respond to an immune checkpoint blockade that targets the checkpoint proteins PD-1 and PD-L1 -- but it is not perfect. Small numbers of patients without PD-L1 in their tumors can also respond to immunotherapy, so we need to know more about what is driving their tumor immunity.”