The use of the FDA-approved checkpoint inhibitor pembrolizumab in clinical practice—for previously treated unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) endometrial cancer (EC), and in combination with lenvatinib for previously treated recurrent or metastatic microsatellite stable (MSS) EC—has not been extensively studied following its approval, according to researchers. Therefore, they assessed the frequency of pembrolizumab use among patients undergoing treatment for EC between May 2012 and June 2021. Among 1,541 patients screened for EC, 634 had MSS status and 179 had MSI-H/dMMR status. In 634 patients with MSS who were screened for EC, 42 met FDA criteria for pembrolizumab use, among whom (61.9%) received pembrolizumab and lenvatinib. Among those with MSS EC who did not receive pembrolizumab and lenvatinib, 12 were treated with chemotherapy, three were enrolled in clinical trials, and one was lost to follow-up. Among 179 patients with MSI-H/dMMR who were screened for EC, 16 met FDA criteria for pembrolizumab use, with 81.2% receiving pembrolizumab. The three patients with MSI EC who did not receive pembrolizumab were treated with chemotherapy. “Immunotherapy is underutilized in patients with advanced EC, where the clear, proven benefit has been noted,” the researchers wrote. “There is an opportunity to improve the identification of eligible patients and increase the use of checkpoint inhibitors in EC with continued education.”