The approval of VYLOY (zolbetuximab-clzb) by the FDA in October 2024 and the European Commission in September 2024 represents the first targeted therapy directed against claudin 18.2 (CLDN18.2) for advanced gastric and gastroesophageal junction (GEJ) adenocarcinoma24. This chimeric monoclonal antibody targets CLDN18.2, a tight junction protein selectively expressed on gastric epithelial cells and retained in approximately 38% of gastric and GEJ cancers17. Through antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity mechanisms, zolbetuximab offers a biomarker-driven therapeutic option for patients with HER2-negative disease9. This review synthesizes the pivotal trial evidence, safety profile, diagnostic considerations, and clinical positioning to guide adoption in first-line treatment.
Evidence Base and Efficacy
The regulatory approval of VYLOY rests on two global, randomized, double-blind Phase 3 trials—SPOTLIGHT and GLOW—which enrolled 565 and 507 patients, respectively, across more than 215 centers in 20 countries including the United States, European Union, and China56. Both studies restricted enrollment to treatment-naïve patients with locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma confirmed to be HER2-negative and CLDN18.2-positive, defined as moderate-to-strong membranous CLDN18 staining in at least 75% of tumor cells by immunohistochemistry using the VENTANA CLDN18 (43-14A) RxDx Assay in central testing 256.
SPOTLIGHT evaluated zolbetuximab plus mFOLFOX6 (modified fluorouracil, leucovorin, and oxaliplatin) versus placebo plus mFOLFOX6. The trial met its primary endpoint of progression-free survival and demonstrated a statistically significant improvement in overall survival, a key secondary endpoint. Median progression-free survival (PFS) extended from 8.7 months in the control arm to 10.6 months with zolbetuximab (hazard ratio 0.751, 95% CI 0.598–0.942; p=0.0066), representing an approximately 25% reduction in the risk of disease progression or death 25. Overall survival (OS), the key secondary endpoint, improved from 15.5 months to 18.2 months (hazard ratio 0.750, 95% CI 0.601–0.936; p=0.0053), translating to an absolute gain of 2.7 months and comparable relative risk reduction25. Twenty-four-month OS rates demonstrated sustained benefit, with 37.7% of zolbetuximab-treated patients alive compared to 29.1% in the placebo group16.
GLOW tested zolbetuximab plus CAPOX (capecitabine and oxaliplatin) against placebo plus CAPOX in a parallel design. Median PFS increased from 6.8 months to 8.2 months (hazard ratio 0.687, 95% CI 0.544–0.866; p=0.0007), reflecting an approximately 31% reduction in the risk of disease progression or death 26. Median OS improved from 12.2 months to 14.4 months (hazard ratio 0.771, 95% CI 0.615–0.965; p=0.0118), yielding a 2.2-month absolute survival advantage26. Objective response rates were numerically higher with zolbetuximab in GLOW (53.8% versus 48.8%), though not statistically significant, suggesting the survival benefit derived primarily from disease control rather than tumor shrinkage6.
A meta-analysis pooling three randomized controlled trials (1,233 patients) confirmed the consistency of these findings, reporting pooled hazard ratios of 0.64 for PFS and 0.72 for OS, both favoring zolbetuximab with high statistical significance8. Health-related quality of life analyses from SPOTLIGHT indicated no clinically meaningful deterioration in global health status or time to deterioration between treatment arms, suggesting that the observed efficacy gains were not associated with a clear worsening of patient-reported outcomes in the trial setting 16. The retrieved materials did not provide detailed subgroup analyses stratified by PD-L1 combined positive score (CPS), geographic region, or metastatic burden, limiting the ability to identify differential benefit in these populations1.
Safety and Tolerability
The safety profile of VYLOY is dominated by gastrointestinal adverse events, superimposed on the known toxicities of platinum-fluoropyrimidine chemotherapy. Across the pooled SPOTLIGHT and GLOW populations, the most common treatment-emergent adverse events (TEAEs) of all grades were nausea (82% with mFOLFOX6, 69% with CAPOX), vomiting (67% and 66%, respectively), fatigue, decreased appetite, and diarrhea356. Grade 3 nausea occurred in 16% of patients receiving zolbetuximab with mFOLFOX6 and 9% with CAPOX, while Grade 3 vomiting affected 16% and 12%, respectively3.
Nausea led to permanent discontinuation in 3.4% of patients and dose interruption in 28%, with vomiting causing discontinuation in 3.8% and interruption in 28%3. These rates underscore the importance of proactive antiemetic protocols, particularly during initial treatment cycles when gastrointestinal symptoms are most pronounced56. Hypersensitivity and infusion-related reactions occurred in 18% and 3.2% of patients, respectively, with Grade 3 or higher severity in 2% and 0.4%3. Permanent discontinuation due to hypersensitivity was uncommon (1.3%), including rare anaphylactic reactions (0.4%)3.
Serious TEAEs were reported in approximately 45–48% of zolbetuximab-treated patients, comparable to placebo arms (43.5–49.8%), with no new safety signals emerging in pooled analyses5616. The most common serious events included vomiting, nausea, neutropenia, febrile neutropenia, and decreased appetite2. Laboratory abnormalities of Grade 3 or higher, particularly decreased neutrophil count, decreased leukocyte count, and decreased hemoglobin, reflected the myelosuppressive effects of the chemotherapy backbone3. Drug-related deaths occurred in 2.1% of zolbetuximab recipients versus 2.3% of controls in pooled analyses, indicating a balanced fatal event rate16.
The retrieved materials provided regimen-specific discontinuation and dose-interruption information for VYLOY, but did not provide sufficient detail on relative dose intensity or all backbone-specific toxicity differentials beyond the reported adverse-event summaries. Similarly, cumulative oxaliplatin-related peripheral neuropathy rates were not separately quantified for zolbetuximab-containing regimens1. From an operational standpoint, infusion center preparedness for early-onset nausea and vomiting, including standardized antiemetic prophylaxis and patient education, is critical to maintain treatment adherence and optimize dose delivery.
Diagnostics and Patient Selection
VYLOY's indication is restricted to tumors demonstrating CLDN18.2 positivity, defined as at least 75% of viable tumor cells exhibiting moderate-to-strong (2+ or 3+) membranous staining by immunohistochemistry23. The VENTANA CLDN18 (43-14A) RxDx Assay received simultaneous approval as the companion diagnostic device, employing mouse monoclonal anti-claudin 18 antibody (clone 43-14A) with OptiView DAB detection on formalin-fixed, paraffin-embedded tissue212.
Approximately 38% of patients with locally advanced unresectable or metastatic gastric or GEJ adenocarcinoma meet the 75% positivity cutoff used in SPOTLIGHT and GLOW, based on global screening data from these trials1712. When any detectable CLDN18.2 expression is considered (lower thresholds), approximately 70% of advanced gastric and GEJ cancers demonstrate some degree of staining12. However, prior studies suggested enhanced therapeutic benefit with very high expression levels, validating the 75% threshold for regulatory approval13.
Intratumoral heterogeneity poses a practical challenge, with 33–40% of gastric cancers exhibiting variable CLDN18.2 expression within the tumor mass13. Discordance between primary tumor and metastatic sites occurs in 20–25% of cases, raising questions about optimal biopsy site selection13. The retrieved materials did not address concordance rates between primary and metastatic samples in the pivotal trials, turnaround times for testing, or standardized pre-analytic protocols to minimize variability1. Reflex testing at diagnosis, alongside routine HER2 and PD-L1 assessment, is advisable to avoid treatment delays in newly diagnosed metastatic disease.
Comparative Clinical Context and Adoption Scenarios
Within the controlled trials, chemotherapy alone yielded median OS of 15.5 months with mFOLFOX6 (SPOTLIGHT) and 12.2 months with CAPOX (GLOW), providing internal benchmarks against which the 2.2–2.7-month OS gains with zolbetuximab can be contextualized256. These absolute improvements, coupled with 22–27% relative risk reductions, meet the threshold for clinical meaningfulness in advanced disease.
Cross-trial comparison with immune checkpoint inhibitor-based regimens requires caution but provides perspective. In CheckMate 649, nivolumab plus chemotherapy demonstrated a hazard ratio of 0.70 for OS in the PD-L1 CPS ≥5 population, with 21% of patients alive at 36 months versus 10% with chemotherapy alone10. In the China subgroup of KEYNOTE-859, pembrolizumab plus chemotherapy achieved a median OS of 15.9 months versus 12.2 months (hazard ratio 0.68) in HER2-negative gastric cancer11. A 2024 network meta-analysis comparing eight first-line regimens (6,455 patients) found no statistically significant differences in OS or PFS between anti-PD-1 agents and anti-CLDN18.2 therapy, though toxicity profiles differed15.
The most compelling adoption scenario for VYLOY centers on newly diagnosed, treatment-naïve patients with HER2-negative, CLDN18.2-positive (≥75% cutoff) gastric or GEJ adenocarcinoma, where addition to mFOLFOX6 or CAPOX confers PFS and OS improvement without compromising quality of life16. The flexibility to combine with either oxaliplatin-based backbone enhances applicability across institutional preferences and patient comorbidities. Marginal or uncertain benefit scenarios include tumors with CLDN18.2 expression below the 75% threshold, co-administration or sequencing with PD-1 inhibitors, and patients unable to tolerate intensive gastrointestinal symptom management, for which no supporting data were available in the retrieved materials116.
Emerging Data and Unanswered Questions
Key evidence gaps remain. The retrieved materials did not identify ongoing trials evaluating triplet strategies combining zolbetuximab with chemotherapy and PD-1 inhibitors, nor perioperative or adjuvant applications116. Biomarker-driven questions persist: efficacy at CLDN18.2 expression thresholds below 75%, mechanisms of acquired resistance, predictors of hypersensitivity reactions, and real-world effectiveness outside the controlled trial setting were not addressed in the available sources116. Retreatment strategies after progression on zolbetuximab-containing regimens also lack empiric data1.
Implementation Considerations
Successful adoption requires multidisciplinary coordination. Pathology services should integrate CLDN18.2 IHC testing into reflex algorithms at diagnosis, standardize tissue handling and scoring protocols to ensure reliable interpretation at the 75% cutoff, and establish quality assurance metrics16. Infusion centers must prepare antiemetic protocols tailored to the high incidence of nausea and vomiting, educate nursing staff on hypersensitivity reaction management, and monitor patients closely during initial treatment cycles316.
Regimen selection between mFOLFOX6 and CAPOX backbones can be guided by patient-specific factors such as renal function, neuropathy risk tolerance, and scheduling preferences, as both demonstrated efficacy in combination with zolbetuximab256. The retrieved materials did not provide information on current guideline integration status in the United States, European Union, or China, nor on institutional adoption trajectories following regulatory approval1.
Conclusion
VYLOY (zolbetuximab-clzb) represents a validated, biomarker-driven addition to first-line therapy for HER2-negative, CLDN18.2-positive gastric and GEJ adenocarcinoma, supported by dual Phase 3 trials demonstrating consistent PFS and OS benefits with both mFOLFOX6 and CAPOX backbones256. The safety profile is characterized by manageable gastrointestinal toxicity requiring proactive supportive care, with no new or unexpected safety signals316. Companion diagnostic testing at the 75% CLDN18.2 expression threshold identifies approximately 38% of candidates, underscoring the importance of reflex testing workflows112. Cross-trial and network meta-analysis comparisons provide context but cannot establish comparable efficacy between zolbetuximab-based and PD-1-based regimens; head-to-head data and biomarker-guided sequencing strategies remain areas for future investigation 101115. For centers equipped with robust testing and supportive care infrastructure, VYLOY offers a clinically meaningful survival benefit in a well-defined patient population.