Zolbetuximab + CAPOX in 1L claudin-18.2+ (CLDN18.2+)/HER2− locally advanced (LA) or metastatic gastric or gastroesophageal junction (mG/GEJ) adenocarcinoma: Primary phase 3 results from GLOW.

405736 Background: There is an unmet need for novel targeted therapies that improve outcomes for pts with HER2− LA unresectable or mG/GEJ adenocarcinoma. CLDN18.2 is expressed in normal gastric mucosa cells and retained in most G/GEJ adenocarcinomas. In the phase 3 SPOTLIGHT study, zolbetuximab, a CLDN18.2-targeted chimeric monoclonal antibody, significantly prolonged PFS and OS in pts with CLDN18.2+/HER2− LA unresectable or mG/GEJ adenocarcinoma when combined with mFOLFOX6. GLOW (NCT03653507) is a phase 3 global, double-blind study comparing zolbetuximab or PBO with capecitabine and oxaliplatin (CAPOX) as 1L treatment for this pt population. Methods: Pts with CLDN18.2+ (moderate-to-strong membranous CLDN18 staining in ≥75% tumor cells by IHC)/HER2− LA unresectable or mG/GEJ adenocarcinoma were randomized 1:1 to zolbetuximab IV 800 mg/m 2 (cycle 1, day [D] 1) followed by 600 mg/m 2 (D1 in subsequent cycles) + CAPOX (oral capecitabine 1000 mg/m 2 BID on D1−14 of each cycle; oxaliplatin IV 130 mg/m 2 on D1 of each cycle) for eight 21-day cycles vs PBO + CAPOX; pts continued for >8 cycles with zolbetuximab or PBO, plus capecitabine (investigator decision), until PD or a discontinuation criterium was met. The primary endpoint (EP) was PFS per RECIST v1.1 by IRC. OS was a key secondary EP; other secondary EPs included ORR and safety. Differences between treatment arms in PFS and OS were tested by stratified log-rank tests; OS was tested if PFS was significant. Results: 507 pts were randomized 1:1 to zolbetuximab + CAPOX (N = 254) or PBO + CAPOX (N = 253). Both PFS (median 8.21 vs 6.80 mo, HR 0.687, P=0.0007) and OS (median 14.39 vs 12.16 mo, HR 0.771, P=0.0118) were significantly prolonged with zolbetuximab + CAPOX (Table); in pts with measurable disease, ORR (95% CI) was 53.8% (46.58−60.99) vs 48.8% (41.76−55.84) in zolbetuximab vs PBO arm. The most common TEAEs with zolbetuximab + CAPOX were nausea (68.5% vs 50.2% in zolbetuximab vs PBO arm), vomiting (66.1% vs 30.9%), and decreased appetite (41.3% vs 33.7%); serious TEAEs (47.2% vs 49.8%), grade ≥3 TEAEs (72.8% vs 69.9%), and drug-related TEAEs leading to death (2.4% vs 2.8%) were similar in both arms. Conclusions: Targeting CLDN18.2 with zolbetuximab combined with CAPOX significantly prolonged PFS and OS in 1L pts with CLDN18.2+/HER2− LA unresectable or mG/GEJ adenocarcinoma. These results align with those observed in SPOTLIGHT and establish zolbetuximab + chemotherapy as a potential new standard-of-care option for these pts. Clinical trial information: NCT03653507 . [Table: see text]