Immunotherapy is an innovative breast cancer treatment that helps your own immune system find and destroy cancer cells. Breast cancer cells have certain proteins that hide them or shield them from the body's t-cells, which are immune system cells that find and kill unwanted substances in the body. Immunotherapy works by inhibiting these proteins, allowing your immune system to find and attack cancer cells, and to produce more cancer-fighting t-cells.

How Does Immunotherapy Work? 
The immunotherapy drugs used to treat breast cancer are called immunomodulators, or checkpoint inhibitors. A checkpoint protein is a protein in your body that helps t-cells differentiate healthy cells from foreign cells. T-cells have a checkpoint protein called PD-1 that attaches to it's counterpart, PD-L1, which is expressed by many of your own healthy cells. However, some breast cancer cells overexpress PD-L1,  allowing the cancer cells to pose as healthy cells and shield themselves from t-cells. The checkpoint inhibitors described below block PD-1 from binding to PD-L1, allowing t-cells to find and kill the previously shielded cancer cells.

There are two immunotherapy drugs approved for breast cancer treatment: Pembrolizumab (Keytruda) and Dostarlimab (Jemperli). 


Pembrolizumab (Keytruda)
Keytruda is a checkpoint inhibitor 
that works by inhibitng the PD-1 protein, allowing t-cells to attack cancer cells. 
Who is eligible to take keytruda? 
Keytruda is meant for those with triple negative breast cancer (TNBC) whose cancer cells express PD-1. 

It may be used: 
-before/after surgery to reduce recurrence risk 
-for metastatic TNBC (stage IV) 
-for local recurrence

Possible Side Effects of Keytruda: 
-fatigue
-muscle pain
-rash
-diarrhea
-decrease appetite
-stomach pain
-low thyroid hormone levels 
Serious/rare side effects: 
-infusion reaction (similar to allergic reaction) 
-autoimmune reaction: because immunotherapy deactivates one of the checkpoint proteins that many healthy cells possess, there is a risk that your immune system may start attacking healthy tissue in your body, including your lungs, kidneys, liver, and other organs. This is a rare side effect, but possible. If this happens, you will stop immunotherapy immediately and may need a immunosuppressant. 
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Dostarlimab (Jemperli)
Dostarlimab is a checkpoint inhibitor that can be used on patients with metastatic breast cancer that has a specific DNA marker (dMMR). This drug also targets the PD-1 checkpoint protein. 

Possible Side Effects of Dostarlimab:
-fatigue 
-anemia (low red blood cell count) 
-diarrhea, naseau, vomiting 
severe side effects: 
​-rash (from inflammation of the skin) 
-hormone gland issues 
-autoimmune reaction: because immunotherapy deactivates one of the checkpoint proteins that many healthy cells may possess, there is a risk that your immune system may start attacking healthy tissue in your body, including your lungs, kidneys, liver, and other organs. This side effect is rare, but possible. If this happens, you will likely immediately stop immunotherapy and may need a immunosuppressant.