FDA Approves Keytruda for Adults, Children with MSI-H or dMMR Solid Cancers

After granting an accelrated approval to Keytruda years ago, the FDA now gave a full approval to the drug for MSI-H or dMMR solid cancers

The Food and Drug Administration (FDA) approved Keytruda (pembrolizumab) for the treatment of adults and children with unresectable (not able to be removed via surgery) or metastatic microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors that have gotten worse after treatment and have no other satisfactory treatment options, according to Merck, the manufacturer of the immunotherapy agent.

Keytruda was initially granted an accelerated approval in 2017 that was contingent on further follow-up. Now, based on findings from the KEYNOTE-158, KEYNOTE-164 and KEYNOTE-051 trials — which collectively include children and adults with more than 30 types of cancer — the FDA granted the drug a full approval.

“This approval reinforces the important role of Keytruda in certain patients with MSI-H or dMMR solid tumors facing a variety of cancers,” said Dr. Luis A. Diaz, Jr., head of the division of solid tumor oncology at Memorial Sloan Kettering Cancer Center in New York, in a press release issued by Merck. “These data also further underscore the need for biomarker testing to identify patients who may be eligible for this therapy.”

Biomarker testing is method of testing tumors to determine if they have any mutations or other actionable characteristics, known as biomarkers, that can be targeted by certain drugs. In this case, clinicians would be looking for MSI-H or dMMR status, which occur when cells’ DNA has defects in the way it fixes errors.

Prior research has shown that immune checkpoint inhibitors such as Keytruda tend to work well in treating patients with MSI-H or dMMR solid tumors. The recent findings of the KEYNOTE studies that led to this approval show that as well.

In a pooled analysis of the three trials, one-third (33.3%) of patients responded to treatment with Keytruda, including a 10.3% complete response rate, meaning that there were no signs of cancer, after a median follow-up of 20.1 months. Among the patients who responded to treatment, 77% had responses lasting 12 months or longer, and 39% had responses lasing 36 months or longer. The average duration of response (time from treatment until disease got worse) was 63.2 months.

MSI-H/dMMR status is most commonly found in colorectal cancer. Among patients with colorectal cancer, 34% responded to Keytruda, with a duration of response ranging from 4.4 to 58.5 months.

In patients with other MSI-H/dMMR solid tumors, which included other gastrointestinal cancers, gynecologic cancers, breast cancer, sarcoma, neuroendocrine cancers, lung cancer, genitourinary cancers, head and neck cancers and others, there was a response rate of 33%. Responses in this group ranged from 1.9 to 63.9 months.

Keytruda is an immunotherapy drug that works by inhibiting a protein found on cancer cells that helps them hide from the immune system. In doing so, the immune system is activated to find and fight cancer. With this mechanism of action comes the possibility for immune-related side effects that can affect one or more organs/systems in the body.

Potential immune-related side effects include pneumonitis (inflammation of lung tissue), colitis (swelling of the colon), hepatitis, endocrinopathies (disease affecting the endocrine gland), nephritis (inflammation of the kidneys), skin-related reactions, solid organ transplant rejection and complications of allogeneic hematopoietic stem cell transplantation. It is important that patients tell their health care team of any side effects that they are experiencing so that they can be addressed quickly and effectively.

READ MORE: Immunotherapy Side Effects: Know What to Look For

"Today’s approval builds on the 2017 accelerated approval of Keytruda as the first immunotherapy with a tumor agnostic indication and supports the role of Keytruda as an effective immunotherapy option based on a pan-tumor predictive biomarker," said Dr. Scot Ebbinghaus, vice president of global clinical development for Merck Research Laboratories, in the release.

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