Does Immunotherapy Treat Breast Cancer?
By Devon Carter
Can immunotherapy treat breast cancer? For certain patients, the answer is yes.
Two immunotherapy drugs — atezolizumab and pembrolizumab — are approved by the Food and Drug Administration (FDA) for patients with metastatic triple-negative breast cancer. Both of these are immune checkpoint inhibitors, the most common type of immunotherapy.
To understand how these drugs work, which breast cancer patients are benefiting and what’s ahead with research, we spoke with Clinton Yam, M.D.
How does immunotherapy work to treat triple-negative breast cancer?
Immunotherapy treats cancers by waking the immune system’s natural ability to defend the body from infection and disease, including cancer. T cells are a type of immune cell that help lead the immune system’s response to an illness.
PD-L1 is a protein that can be found on the surface of cancer cells and/or immune cells. It binds with a partner protein called PD-1 that’s on the surface of a T cell. But this bond turns off the T cell and allows the cancer cell to hide from the T cell. Immune checkpoint inhibitors take off this brake, which increases the likelihood that the T cells will attack and destroy the cancer cells.
Is immunotherapy an option for all patients with triple-negative breast cancer?
Unfortunately, no. Because atezolizumab and pembrolizumab interfere with the bond between PD-1 and PD-L1, immune checkpoint inhibitors are currently only used to treat patients with triple-negative breast cancer where the PD-L1 protein is found on the cancer and/or immune cells within the tumor. We determine if a patient has a high expression of PD-L1 through an immunohistochemistry test. This is performed on tissue that’s removed during biopsy. If the PD-L1 protein is not found on the cancer cells and/or immune cells within the tumor, PD-L1 immune checkpoint inhibitors won’t be effective.
Secondly, these drugs are currently only approved for use in patients with advanced disease. The cancer must have returned after initial treatment and not eligible for surgery, or it must have spread to other parts of the body. This is known as metastatic disease.
Lastly, immunotherapy may worsen symptoms of autoimmune disorders like lupus and rheumatoid arthritis, so these drugs aren’t typically used in women with these chronic illnesses.
What are the side effects of immunotherapy in patients with breast cancer?
Immunotherapy side effects are the same, regardless of the type of cancer being treated.
Immunotherapy increases the ability of the immune system to attack cancer cells, but it also increases the chances that the immune system will affect normal cells. This can cause inflammation throughout the body, which can lead to side effects, such as skin changes, cough, chest pain and diarrhea. In some cases, these side effects can be debilitating, depending on the organ(s) involved.
For example, if the thyroid gland is affected, the patient may develop a condition called hypothyroidism (low thyroid hormone) and may need thyroid hormone replacement in the future. In rare but extreme cases, liver or kidney failure can develop.
When treating breast cancer, is immunotherapy used alone or in combination with other therapies?
Right now, immune checkpoint inhibitors are used in combination with chemotherapy to treat metastatic triple-negative breast cancer.
However, there are ongoing clinical trials studying other combinations. For example, researchers are trying to find out if immunotherapy is more effective when combined with targeted therapies, such as PARP inhibitors. One challenge with treating breast cancer with immunotherapy is that immune cells have a harder time infiltrating the tumors. By combing immune checkpoint inhibitors with targeted therapies, we hope to help the immune cells better enter the tumor and, therefore, make these drugs an effective treatment option for more patients.
There is also hope that we may be able to use therapeutic vaccines to train the immune system to fight cancer.
Lastly, we know that radiation therapy helps jump-start the immune system. Through clinical trials, researchers are exploring how we might optimize immunotherapy by combining it with radiation therapy.
What are the immunotherapy options for patients with other breast cancer subtypes?
Clinical trials are working to expand the use of immunotherapy to more patients, including those with other stages of triple-negative breast cancer, as well as other breast cancer subtypes.
If you’re interested in immunotherapy options for breast cancer treatment, I encourage you to talk with your care team about clinical trial options. You may find a clinical trial opportunity that can give you access to immunotherapy and also enable you to pay it forward for future cancer patients.