Zolbetuximab Combined with EOX As First-Line Therapy in Advanced CLDN18.2+gastric (G) and Gastroesophageal Junction (GEJ) Adenocarcinoma: Updated Results from the FAST Trial.

16 Background: Physiologically, the tight junction protein CLDN18.2 is present only in the gastric mucosa. Upon malignant transformation, CLDN18.2 epitopes are exposed on the cell surface and accessible to targeted therapy. Zolbetuximab (formerly IMAB362) is a chimeric mAb that mediates specific killing of CLDN18.2+ cancer cells through immune effector mechanisms; single-agent activity has been reported in G/GEJ cancer. Methods: Patients (pts) with advanced HER2-negative (HER–) G/GEJ cancer with CLDN18.2 expression of ≥ 2+ staining intensity with the anti-CLDN18 43-14A mAb in ≥ 40% tumor cells were eligible (NCT01630083). Patients were randomized 1:1 to receive first-line EOX ± zolbetuximab (loading dose 800 mg/m2, then 600 mg/m2) Q3W. The study was extended with an exploratory arm of 1000 mg/m2 zolbetuximab + EOX Q3W (data not presented). Primary endpoint was PFS; secondary endpoints included OS, ORR, and safety/tolerability. Results: A total of 161 pts (G, n = 128; GEJ, n = 27; esophagus n = 6) were randomized to receive zolbetuximab (800/600 mg) + EOX (n = 77) or EOX alone (n = 84). In all, 45% of pts had diffuse type histology per Lauren’s classification. Median PFS was longer with zolbetuximab + EOX (7.5 mo) versus EOX alone (5.3 mo; P < 0.0005; HR 0.44; 95% CI 0.29, 0.67). Median OS (13 vs 8.4 mo; P = 0.0008; HR 0.56; 95% CI 0.40, 0.79) and ORR (39 vs 25%; P = 0.022) were also significantly higher with zolbetuximab + EOX versus EOX alone. Increased efficacy was more pronounced in pts with high CLDN18.2 expression (≥ 2+ staining intensity in ≥ 70% tumor cells). Zolbetuximab + EOX was generally well tolerated. Most AEs considered related to zolbetuximab and EOX (ie, nausea, vomiting, neutropenia, anemia) were of grade ≤ 2 severity; there was no significant increase in grade ≥ 3 events with the addition of zolbetuximab to EOX. Conclusions: Addition of zolbetuximab to first-line chemotherapy resulted in significantly longer PFS and OS and higher ORR with manageable toxicity. A phase III trial is evaluating the combination of zolbetuximab plus mFOLFOX6 as first-line treatment of CLDN18.2+/HER2-negative, advanced/metastatic G or GEJ adenocarcinoma (NCT03504397). Clinical trial information: NCT01630083.