Immunotherapy drugs help your immune system recognize and attack cancer cells. Checkpoint inhibitors are the most common type of immunotherapy drugs. These drugs “take the brakes off” the natural factors that limit how the immune system can control tumor cells.

Pembrolizumab, also known as Keytruda, is a checkpoint inhibitor immunotherapy drug used for some early triple negative breast cancers at high risk of recurrence.

Triple negative breast cancer is:

• Estrogen receptor-negative (ER-negative)
• Progesterone receptor-negative (PR-negative), and
• HER2-negative

Pembrolizumab is given with chemotherapy before breast surgery (called neoadjuvant therapy). Studies show adding pembrolizumab to neoadjuvant chemotherapy helps shrink the tumor and may lower the risk of recurrence.

Pembrolizumab is given through an IV into a vein every 3 to 6 weeks for up to one year. You may get a smaller dose once every 3 weeks or a larger dose once every 6 weeks.

Before you begin treatment with pembrolizumab, talk with your health care team about possible side effects and how to manage them.

Some possible side effects of pembrolizumab include fatigue, muscle pain, decreased appetite, itchiness, diarrhea, nausea, rash and constipation. Pembrolizumab can also cause hormone gland problems, severe colitis, which is inflammation of the colon, and liver problems.

In rare cases, pembrolizumab can cause lung inflammation, which can lead to death. Tell your health care provider right away if you have shortness of breath or other breathing problems while taking this drug.

If you’ve been diagnosed with early triple negative breast cancer, talk with your health care provider about whether pembrolizumab is an option for you.

If you begin immunotherapy treatment and throughout the time you’re getting it, let your health care team know how you’re feeling. They may be able to treat many of these side effects.

For more information, visit the Immunotherapy page within the Treatment section of komen.org.

Pembrolizumab is also used to treat HER2-positive metastatic breast cancer. For more information, see the Living with Metastatic Breast Cancer chapter of this tool.