755P - Retifanlimab in patients with recurrent microsatellite instability-high (MSI-H) or deficient mismatch repair (dMMR) endometrial cancer: Final results from the POD1UM-101 study (Cohort H)

Background

Retifanlimab (Zynyz^TM) is a programmed death receptor-1 (PD-1)–blocking antibody recently approved in the United States for the treatment of adult patients with metastatic or recurrent locally advanced Merkel cell carcinoma. POD1UM-101 (NCT03059823) is an ongoing first-in-human dose finding and cohort expansion study in patients with advanced solid tumours. We have previously reported significant clinical activity with safety for retifanlimab representative of the class in the MSI-H or dMMR endometrial cancer expansion cohort (Berton D, SITC 2021). We present final study results.

Methods

Eligible patients had histologically proven, unresectable recurrent/metastatic MSI-H or dMMR endometrial cancer, Eastern Cooperative Oncology Group performance status (ECOG PS) ≤1, disease progression during or following 1 to ≤5 prior systemic treatments, measurable disease (per RECIST v1.1), and were naïve to prior immune checkpoint inhibitors. MSI-H and dMMR status were centrally confirmed. Patients received retifanlimab 500 mg every 4 weeks for up to 2 years. The primary study endpoint was safety. Confirmed best overall response and duration of response were evaluated by independent central reviewer (ICR).

Results

A total of 76 patients with centrally confirmed MSI-H (65 [85.5%]) or dMMR (11 [14.5%]) disease were enrolled, with the last patient initiating treatment on 29 December 2020. Median age was 67 (range 49–88) years, 70 (92%) had endometrioid histology, 67 (88%) had metastatic disease, and 61 (80%) had visceral metastases. Most patients had received prior radiotherapy (54 [71%]) or surgery (68 [90%]). All patients except for one, had received prior chemotherapy for advanced disease with 33 (43.4%) patients receiving ≥2 prior systemic therapies. The overall response rate by ICR was 43% (95% CI: 32–55). Final results for this cohort including safety and secondary efficacy endpoints will be presented.

Conclusions

Retifanlimab has shown notable clinical activity in previously treated MSI-H or dMMR endometrial cancer, which is consistent with other checkpoint immunotherapies.

Clinical trial identification

NCT03059823, EudraCT 2017-000865-63.

Editorial acknowledgement

Envision Pharma Group (Philadelphia, PA), funded by Incyte Corporation (Wilmington, DE).

Legal entity responsible for the study

Incyte Corporation (Wilmington, DE).

Funding

Incyte Corporation, Wilmington, DE.

Disclosure

P. Pautier: Financial Interests, Institutional, Other, Travel & Honoraria: AstraZeneca, MSD, Tesaro; Financial Interests, Institutional, Other, Travel: Novartis; Financial Interests, Institutional, Advisory Board: AstraZeneca, Novartis, Tesaro. D. Lorusso: Financial Interests, Institutional, Advisory Role, Consultancy: Novartis, PharmaMar; Financial Interests, Institutional, Advisory Board, and invited speaker: AstraZeneca, Clovis Oncology, Genmab, GSK, Immunogen, MSD, Seagen; Financial Interests, Institutional, Other, ENGOT trial with institutional support for coordination: Clovis Oncology, Corcept, Genmab, Immunogen, MSD; Financial Interests, Research Grant, Grant for founding academic trial: Clovis Oncology, GSK, MSD. C. Gennigens: Financial Interests, Institutional, Research Grant: AstraZeneca; Financial Interests, Institutional, Advisory Role: GSK, Ispen, MSD; Financial Interests, Institutional, Other, Honoraria: AstraZencea, Bristol Myers Squibb, GSK; Financial Interests, Institutional, Other, Honoraria and Support for meetings and/or travel: Ispen, MSD, Pfizer, PharmaMar; Financial Interests, Institutional, Advisory Board: AstraZeneca, Bristol Myers Squibb, Eisai, GSK, Ispen, MSD. L. Gladieff: Financial Interests, Advisory Board: AstraZeneca, Clovis Oncology, GSK, MSD; Financial Interests, Other, Honoraria: AstraZeneca, GSK, MSD, PharmaMar, Roche ; Financial Interests, Funding, Congress funding: GSK, PharmaMar, Roche, Viatris. J. Bowman, C. Tian, M. Cornfeld: Financial Interests, Institutional, Full or part-time Employment: Incyte; Financial Interests, Institutional, Stocks/Shares: Incyte. T. Van Gorp: Financial Interests, Institutional, Advisory Board: AstraZeneca, GSK, MSD, Tubulis; Financial Interests, Institutional, Research Grant: Amgen, Roche, AstraZeneca; Financial Interests, Institutional, Invited Speaker: GSK. All other authors have declared no conflicts of interest.