Immunotherapy is the treatment of a disease by changing the immune system. It was believed in the past that breast cancer did not trigger an immune response. Immune response is the reaction of cells of the immune system against a foreign substance that is not recognized as a part of the body. In early 2018, researchers at the University of Washington in Seattle published a study assessing the benefits and potential future of immunotherapy as a form of treatment for breast cancer.
In the last decade, after the detection of an immune response in breast cancer patients, there have been numerous studies that have considered immunotherapy a possible treatment for this type of cancer. A research conducted on women 6 months prior to a breast cancer diagnosis showed high rates of T-cells (a type of white blood cell) against tumor associated proteins in women who would go on to develop breast cancer. Immune checkpoint inhibitor therapy is a mechanism that uses drugs to block certain proteins which prohibit immune cells from killing cancer cells. These agents allow T-cells to recognize cancer cells, and limit tumor growth by dividing and growing themselves.
Research studies have shown that with the progression of cancer, the development of antigens (substances that trigger an immune response) diminishes, reducing immune response. This implied that in order to come up with a proper immunotherapeutic mechanism, researchers must focus on developing strategies that reverse this effect and increase immune response that promotes tumor destruction. One of the first breast cancer associated antigens was the MUC-1 (Human Mucin-1) protein. T-cells related to this protein were in low number in patients with the disease. So, boosting these numbers would be a potential therapeutic mechanism.
It should be noted that despite recent discoveries, breast cancer is still a poor producer of immune response. Tumor infiltrating lymphocytes (TIL), another type of white blood cells infiltrate tumor tissues and cause direct physical contact between them, which results in the physical destruction of tumor cells. However, its occurrence and concentration varies based on the type of breast cancer.
Studies are currently ongoing to identify factors that identify the patients who are most likely to benefit from immune checkpoint inhibitor therapies. This is aided by the fact that despite fluctuating amounts, TILs are always present to some extent. So, one strategy for successful patient identification is to increase the number of TIL beforehand. Immunization has been found as a possible way of accomplishing this. Research has shown that vaccine induced T-cells can travel to the tumor and induce an increase in TIL. Currently, there are several vaccines under development to target multiple breast cancer antigens at the same time to make treatment more effective.
In addition to immunization, standard therapies like radiation and chemotherapy can also increase the amount of TIL. As we understand more immune response inducing effects of traditional treatment methods, we can use them more effectively. Thus, the immune environment of the tumors can be used to combine standard and novel therapeutic strategies to develop more effective treatments. Research on such methodologies is still a field in progress and there is much to learn before we can use the knowledge of immune response in breast cancer cells to improve treatment approaches.
Reference: Disis, M.L., Stanton, S.E. 2018. Immunotherapy in Breast Cancer: An Introduction. The Breast 37:196-199.