In some women with heavily pretreated locally advanced or metastatic endometrial cancers, treatment with the immune checkpoint inhibitor pembrolizumab (Keytruda) produced partial, durable responses, investigators reported.
The women were participants in the KEYNOTE-028 trial, a multicohort, open-label phase Ib basket trial of patients with advanced solid tumors positive for programmed death ligand 1 (PD-L1). Of 24 women with PD-L1-positive endometrial tumors, 3 (13%) had confirmed partial responses, and 2 of these patients remained on therapy with a continued response at the time of data cutoff, reported Patrick A. Ott, MD, PhD, of Dana-Farber Cancer Institute, Boston, and his colleagues.
“[T]he results from the KEYNOTE-028 trial presented herein indicate that pembrolizumab shows promise as a treatment for advanced endometrial cancer, a disease for which current treatment options are limited,” they wrote (J Clin Oncol. 2017 May 10; doi: 10.1200/JCO.2017.72.5952).
Patients with advanced endometrial cancer have a poor prognosis, with 5-year survival rates below 50% for patients with lymph node metastases, and less than 20% for those with distant metastases or disease that has spread to the peritoneum, the investigators noted.
“Treatment options for patients presenting with advanced disease are limited, with no consensus on a standard regimen. Similarly, no optimal therapy for patients who experience progression during first-line therapy has been identified, with second-line chemotherapeutic options producing only modest activity,” they wrote.
PD-L1 was shown to be expressed on 83% of primary endometrial tumors and 100% of metastatic endometrial cancers in one study (Cancer Immunol Immunother. 2014;63[6]:545-57), suggesting that could be a viable target in this difficult-to-treat disease, noted Dr. Ott and his colleagues.
In their study, 24 women with locally advanced or metastatic PD-L1–positive endometrial cancer who had experienced progression after standard therapy were treated with pembrolizumab 10 mg/kg every 2 weeks for up to 24 months or until disease progression or unacceptable toxicity. As noted, 3 of the 24 patients met the primary efficacy endpoint of objective response rate by Response Evaluation Criteria in Solid Tumors (RECIST; version 1.1) with a partial response, with the median duration of response (a secondary endpoint) not reached at the time of data cutoff on Feb. 17, 2016.
Three other patients (13%) had stable disease, with a median duration of 24.6 weeks.
Safety, also a secondary endpoint, was comparable to that seen in other studies with pembrolizumab. Four patients had grade 3 treatment-related adverse events (AEs). There were no grade 4 AEs of any kind, no immune-mediated AEs of any grade, and no treatment-related deaths.
One of the patients who had a partial response was found through genomic profiling to have a polymerase E, or POLE mutation, and this patient had a rapid improvement after starting on pembrolizumab, with the response lasting longer than 14 months.
“These exceptional results support the theory that the presence of POLE mutations may aid in identifying patients for whom pembrolizumab may be particularly effective, a concept that should be investigated further,” wrote Dr. Ott and his colleagues.
Merck Sharp & Dohme sponsored the study. Dr. Ott and multiple coauthors disclosed institution research funding, honoraria, consulting, or advising with the company, and three are Merck employees..