Phase 2 study of cabozantinib (Cabo) and pembrolizumab (Pembro) in metastatic gastric/gastroesophageal adenocarcinoma (mGEA) resistant or refractory to immune checkpoint inhibitors (ICI).

Abstract

315 Background: Most mGEA patients (pt) progress on therapy including ICI, with about 5% progression-free at 6 mo (PFS-6) with single agent ICI in later lines of therapy. Alternative therapeutic approaches are needed. Cabo is a multi-tyrosine kinase inhibitor thought to enhance the immunomodulatory effects of ICI. This study reports on safety and efficacy of the combination of Cabo+Pembro in mGEA resistant or refractory to ICI. Methods: Investigator-initiated, single‐arm, single institution, phase 2 study in pts with mGEA after ≥1L of fluoropyrimidine and platinum-containing regimens. Pts with a PD-L1 CPS score ≥10% had also progressed on ICI. Cabo dose was 40mg p.o. daily on days 1 through 21 of a 21‐day cycle, with Pembro 200 mg i.v. on day 1. The primary endpoint was PFS-6, with H0=5%, Ha≥20%, requiring n=27 evaluable pts and n≥4 pts with PFS-6 to reject H0 in favor of Ha. Results: 27 pts were enrolled. Median age 58 years (24-87), female (n=14), ECOG 0/1= 13/14, GC/GEJ= 16/11, Non-Hispanic White/Hispanic/Asian= 12/8/7. The primary endpoint was met with n=6 pts having PFS>6mo. After a median follow-up of 31.4mo (range 3.3-42.5), PFS-6 is 22.2% (95% CI 9.0-39.0). The median PFS and OS are 2.3mo (95% CI 1.7-4.1) and 5.5mo (3.1-14.0), respectively. The most common mutations were TP53 (78.3%) and CDH1/PIK3CA/CTNNB1 (17.4% each). In exploratory analyses, 5/7 (71.4%) pts in the top quartile for PFS had alterations in the cMET-PI3K-AKT pathway. The most common any grade (G) treatment related adverse events (TRAE) were diarrhea (25.9%), fatigue (18.5%), hypertension and muscle cramps (14.8% each). G3-4 TRAE were seen in n=3 pts (Hypertension, Thromboembolic event, esophageal perforation; each n=1). No G5 were observed. Conclusions: The addition of Cabo to Pembro shows clinical benefit in ICI resistant or refractory mGEA with an observed PFS-6 of 22.2%. The regimen appears tolerable with no new safety signals. An exploratory association of alterations in the cMET-PI3K-AKT pathway with prolonged PFS needs to be confirmed in a larger cohort. Clinical trial information: NCT04164979 .