Real World Multi-centre UK Review of Nivolumab Monotherapy in Metastatic Endometrial Cancer With Mismatch Repair Deficiency During COVID-19.

Introduction: Immunotherapy checkpoint inhibition has shown improvement in efficacy and survival in patients with mismatch repair deficient (MMRd) advanced endometrial cancer (mEC) compared to chemotherapy. This is combined with chemotherapy in the first-line setting or as monotherapy in later lines of therapy.

Objective: To assess the efficacy, survival and toxicity of nivolumab monotherapy in metastatic endometrial cancer (mEC) in both first and later lines of therapy as used in the NICE COVID-19 systemic anti-cancer (SACT) guidelines.

Methods: A multi-centre retrospective review of mEC patients with associated MMRd who received nivolumab as per NICE COVID NG161 at 10 NHS cancer centres. Patient demographics, molecular classification and previous treatments were recorded in addition to treatment responses, duration of response, overall survival, progression-free survival and toxicities. Kaplan-Meier curves analyse the survival data.

Results: 52 patients were identified. Median age was 67 (37-81) years. 87.5% of patients had endometrioid histology and 75% were oestrogen receptor (ER) positive. 10.4% patients were p53 mutated. 33.3% of mEC patients were stage IV at diagnosis. 30 (62.5%) patients received nivolumab as first-line mEC therapy. 33 (68.8%) patients received nivolumab 4-weekly. Treatment response was clinician-observed in 34 (70.8%) patients, with 7 (14.5%) more having stable disease. 52%, 45% and 36% of patients were progression-free at 12, 18 and 24months, respectively. 75%, 55% and 47% of patients were alive at 12, 18 and 24 months. There was no significant difference between survival or response whether nivolumab was given in the first line or subsequent lines. 29 (60.4%) patients have discontinued treatment with 23 (44.2%) being due to progressive disease or death. 18 (37.5%) patients developed G1-2 toxicity, and 3 (6.25%) patients discontinued due to G3 toxicity.

Conclusions: This retrospective cohort shows that nivolumab monotherapy has good real-world disease control of mEC patients with MMR deficiency. Toxicity rates were low, and checkpoint monotherapy may be a viable option for selected first-line MMRd mEC patients.