On July 26, 2021, the U.S. Food and Drug Administration (FDA) approved the immunotherapy medicine Keytruda (chemical name: pembrolizumab) plus chemotherapy before surgery, followed by Keytruda alone after surgery to treat early-stage triple-negative breast cancer with a high risk of recurrence (the cancer coming back).
Doctors call treatments given before surgery neoadjuvant treatments and treatments given after surgery adjuvant treatments.
Early-stage triple-negative breast cancer is considered to have a high risk of recurrence if:
- the tumor is between 1 and 2 cm in size and the cancer has spread to the lymph nodes
- the tumor is larger than 2 cm, regardless of whether the cancer has spread to the lymph nodes or not
About triple-negative breast cancer
Triple-negative breast cancer is:
Triple-negative breast cancers are usually more aggressive, harder to treat, and more likely to recur than cancers that are hormone-receptor-positive or HER2-positive. Triple-negative breast cancers don’t usually respond to hormonal therapy medicines or medicines that target the HER2 protein.
Keytruda is a type of immunotherapy medicine known as an immune checkpoint inhibitor. To start an immune response to a foreign invader, the immune system has to be able to tell the difference between cells or substances that are “self” (part of you) and “non-self” (not part of you and possibly harmful). Your body’s cells have proteins on their surfaces or inside them that help the immune system recognize them as “self.”
Some of the proteins that help your immune system recognize “self” cells are called immune checkpoints. Cancer cells sometimes find ways to use these immune checkpoint proteins as shields to avoid being identified and attacked by the immune system.
Immune system cells called T cells roam throughout the body looking for signs of disease or infection. When T cells meet another cell, they analyze certain proteins on the cell’s surface, which helps the T cell identify the cell. If the surface proteins signal that the cell is normal and healthy, the T cell leaves it alone. If the surface proteins suggest the cell is cancerous or unhealthy in another way, the T cell starts an attack against it. Once T cells start an attack, the immune system begins to make more specialized proteins that prevent this attack from damaging normal cells and tissues in the body. These specialized proteins that keep healthy cells and tissues safe are called immune checkpoints.
Immune checkpoint inhibitors target these immune checkpoint proteins and help the immune system recognize and attack cancer cells. Immune checkpoint inhibitors essentially take the brakes off the immune system by blocking checkpoint inhibitor proteins on cancer cells or on the T cells that respond to them.
For example, PD-1 is a checkpoint protein on T cells. PD-L1 is another checkpoint protein found on many healthy cells in the body. When PD-1 binds to PD-L1, it stops T cells from killing a cell. Some cancer cells have a lot of PD-L1 on their surfaces, which stops T cells from killing these cells. Keytruda stops PD-1 from binding to PD-L1 and allows T cells to attack the cancer cells.
In 2020, the FDA approved the combination of Keytruda and chemotherapy to treat unresectable locally advanced or metastatic triple-negative, PD-L1-positive breast cancer. Unresectable means the cancer can’t be removed with surgery.
Keytruda is given as an injection in a doctor’s office every 3 weeks or every 6 weeks, depending on the dose you’re receiving.
Research supporting approval
The most recent FDA approval is based on results from the KEYNOTE-522 study showing that Keytruda plus chemotherapy before surgery, followed by Keytruda alone after surgery, improved event-free survival better than chemotherapy alone in women diagnosed with early-stage triple-negative breast cancer that has a high risk of recurrence.
For this study, the researchers defined event-free survival as the length of time a person lived without:
- the cancer growing
- the cancer coming back in a part of the body away from the breast (distant recurrence)
- receiving a second primary cancer diagnosis
Keytruda side effects
Like most cancer treatments, Keytruda can cause side effects, some of them severe. In the KEYNOTE-522 study, the most common side effects caused by Keytruda were:
- hair loss
- peripheral neuropathy
- mouth sores
- joint pain
- abdominal pain
- loss of appetite
- muscle pain
In the KEYNOTE-522 study, side effects caused 20% of people treated with Keytruda to stop treatment. Overall, 0.9% of people treated with Keytruda in the KEYNOTE-522 study died from treatment-related side effects.
What this means for you
If you’ve been diagnosed with early-stage triple-negative breast cancer with a high risk of recurrence and are deciding on treatments before surgery, you may want to ask your doctor if Keytruda is right for your unique situation.
Learn more about Immunotherapy, including how it works and possible side effects.
To discuss Keytruda and other immunotherapy medicines with others, join the Breastcancer.org Discussion Board forum Immunotherapy - Before, During, and After.
Written by: Jamie DePolo, senior editor
Reviewed by: Brian Wojciechowski, M.D., medical adviser
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