On March 21, 2022, the FDA approved a new indication for the PD-1 inhibitor (a type of immunotherapy) Keytruda (pembrolizumab; from Merck) as monotherapy (only therapy) for the treatment of patients with advanced endometrial carcinoma that is microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR), as determined by an FDA-approved test, in patients whose cancer progressed after systemic therapy and who are not candidates for curative surgery or radiation therapy.
The FDA previously approved the use of Keytruda in combination with Lenvima (lenvatinib) for the treatment of patients with advanced endometrial carcinoma and the MSI-H or dMMR biomarker. This is the first approval of an immunotherapy alone for patients with this type of cancer.
This approval was based on the KEYNOTE-158 clinical trial, a multicenter, open-label, multicohort study of 90 patients with unresectable or metastatic MSI-H or dMMR endometrial carcinoma in cohorts D and K of the study.
The objective response rate with Keytruda alone was 46%, and the average duration of response was not reached, meaning patients were still responding to therapy; of the patients who responded to Keytruda, 68% had a response lasting 1 year or longer, and 44% had a response lasting 2 years or longer.
The most common side effects in the study were fatigue, musculoskeletal pain, rash, diarrhea, fever, cough, decreased appetite, pruritus, dyspnea, constipation, pain, abdominal pain, nausea, and hypothyroidism. The immune-mediated side effects associated with Keytruda include pneumonitis, colitis, hepatitis, endocrinopathies, nephritis, and skin reactions.