On Nov. 13, 2020, the U.S. Food and Drug Administration (FDA) approved the immunotherapy Keytruda (chemical name: pembrolizumab) in combination with 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.
Locally advanced breast cancer is breast cancer that has spread to tissue near the breast, but not to parts of the body away from the breast. Metastatic breast cancer is cancer that has spread to parts of the body away from the breast, such as the bones or liver.
The approval is based on results from the KEYNOTE-355 trial, which showed that Keytruda along with chemotherapy offered better progression-free survival than chemotherapy alone as the first treatment for PD-L1-positive, metastatic triple-negative breast cancer or PD-L1-positive, triple-negative breast cancer that has come back (recurred) in the breast area but can’t be removed with surgery.
“Notably, in KEYNOTE-355, Keytruda was combined with three different chemotherapy regimens: paclitaxel, nab-paclitaxel, or gemcitabine and carboplatin,” said Hope Rugo, M.D., director of Breast Oncology and Clinical Trials Education at the University of California, San Francisco, Helen Diller Family Comprehensive Cancer Center, in a statement. Rugo is also a member of the Breastcancer.org Professional Advisory Board. “The approval of Keytruda in combination with chemotherapy gives physicians an important new option for appropriate patients.”
Progression-free survival is how long a person lives without the breast cancer growing.
Keytruda is a type of immunotherapy medicine called a checkpoint inhibitor.
To start an immune system 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 these 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 a shield 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.
Immune checkpoint inhibitors target 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.
PD-1 is a type of checkpoint protein found 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 surface, which stops T cells from killing these cancer cells. An immune checkpoint inhibitor medicine that stops PD-1 from binding to PD-L1 allows T cells to attack the cancer cells.
Keytruda blocks the PD-1 pathway.
Keytruda is given as a 30-minute infusion, every 3 or 6 weeks, depending on the dosage given at each infusion. The Keytruda infusion is given before the chemotherapy infusion.
About triple-negative breast cancer
Triple-negative breast cancer is:
So the growth of triple-negative disease isn’t driven by the hormones estrogen or progesterone or by the presence of too many HER2 receptors. This means that triple-negative breast cancer doesn’t respond to hormonal therapy (such as tamoxifen or an aromatase inhibitor) or therapies that target HER2 receptors.
About 10% to 20% of breast cancers — more than one out of every 10 — are triple-negative. Triple-negative breast cancer tends to be more aggressive than other types of breast cancer.
Keytruda side effects
Like most cancer treatments, Keytruda can cause side effects, some of them severe. In the KEYNOTE-355 study, 96.3% of people treated with Keytruda and chemotherapy and 95% of people treated with chemotherapy alone had side effects.
Severe side effects (grade 3-5) were seen in 68.1% of people treated with Keytruda and chemotherapy and 66.9% of people treated with chemotherapy alone.
The most common side effects seen in people treated with Keytruda and chemotherapy were:
- hair loss
- loss of appetite
- low white blood cell counts
In the KEYNOTE-355 study, side effects caused 18.1% of people treated with Keytruda and chemotherapy and 11% of people treated with chemotherapy alone to stop treatment.
Two people treated with Keytruda and chemotherapy died from treatment-related side effects.
Immune system-related side effects were seen in 25.6% of people treated with Keytruda and chemotherapy and in 6% of people treated with chemotherapy alone. The most common immune system-related side effect was hypothyroidism (underactive thyroid gland).
What this means for you
If you’ve been diagnosed with locally advanced or metastatic triple-negative breast cancer and are deciding on treatments for the advanced-stage disease, you may want to talk to your doctor about PD-L1 testing on the cancer and whether Keytruda is right for your unique situation.
For more information on immunotherapy medicines, including how they work and their possible side effects, visit the Breastcancer.org Immunotherapy page.
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
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