Immunotherapy drugs help the body’s immune system attack cancer cells. Checkpoint inhibitors are the most widely used 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. Pembrolizumab is used to treat 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 triple negative breast cancer and may lower the risk of breast cancer recurrence.

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

Some possible side effects of pembrolizumab include fatigue, muscle pain, decreased appetite, itchiness, diarrhea, nausea, rash and constipation. Pembrolizumab can cause colitis (inflammation of the intestines), liver problems and hormone gland 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.

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