Q: I was recently diagnosed with breast cancer. The doctor mentioned using immunotherapy. What is immunotherapy, and how does it differ from chemotherapy?
A: Immunotherapy is a newer therapy in the current treatment landscape for breast cancer. It has also been used in treating other cancers, including lung cancer, melanoma and kidney cancer. While chemotherapy targets cells that grow and divide quickly, such as cancer cells, immunotherapy harnesses the body’s immune system to help fight cancer.
To understand how immunotherapy works, you must understand the role of the immune system. The immune system protects the body against any perceived threats, including cancer cells. The immune system is a complex network of substances and cells that are trained to recognize proteins on the surface of other cells as a part of the body (“self”) or as not a part of the body (“nonself”) and possibly harmful.
This mechanism prevents neoplastic cells — cells that have atypical tissue growth — from developing into tumors by destroying them. However, cancer cells can outsmart the immune system. One way they do this is by manipulating the immune mechanism to turn off the body’s response. Essentially, cancer cells disable the immune checkpoints, thereby preventing attack and hindering destruction of cancer cells.
A specific type of immunotherapy was developed to prevent this. Known as a checkpoint inhibitor, also called a PD-1 pathway inhibitor, this treatment aims to prevent this deactivation and increase the body’s anti-tumor immune response.
An immunotherapy agent known as pembrolizumab (Keytruda) has been approved by the Food and Drug Administration for triple-negative breast cancer. To be a candidate for immunotherapy, you must:
- Have high-risk, early-stage triple-negative breast cancer. In this case, pembrolizumab is used with chemotherapy before surgery and continued without chemotherapy after surgery.
- Have locally recurrent unresectable or metastatic triple-negative breast cancer. In this setting, your cancer tissue must express PD-L1 (marker of immune system), which is detected by a test done by a pathologist on your tumor tissue. In this case, pembrolizumab is used with chemotherapy.
Common side effects of pembrolizumab include:
- Respiratory symptoms, such as shortness of breath and cough
- Gastrointestinal symptoms, such as diarrhea, constipation, nausea and vomiting
Pembrolizumab can also:
- Affect liver function tests
- Cause overactive or underactive thyroid or adrenal insufficiency
Most of these side effects are mild to moderate and reversible if detected early and treated in a timely manner. For more-severe side effects, sometimes the immunotherapy drug may need to be temporarily or permanently stopped. Immunosuppressant medications or oral steroids may be used to reduce the immune response and control side effects.
The use of immunotherapy for other subtypes of breast cancer, including hormone-receptor-positive and HER2-positive breast cancer, also is being evaluated. Several clinical trials are underway to investigate the combination of immunotherapy with targeted agents or chemotherapy, or both, across different types of breast cancer.
A cancer vaccine is another type of immunotherapy that is being developed and tested for breast cancer. Cancer vaccines help train the immune system to see and “memorize” particular proteins (antigens) found on the surface of cancer cells. Then the immune system can fight these antigens if encountered in the future. These vaccines are being studied in different breast cancer settings: treating cancer, preventing cancer recurrence and lessening the risk of cancer spreading to another part of the body (metastasis).
The use of immunotherapy to treat people with certain breast cancers is promising. For many, immunotherapy can be a valuable tool. Speak with your health care provider about the pros and cons for your situation. You also can learn more about clinical trials using immunotherapy at Mayo Clinic’s website.