Antibody-drug conjugates in gastric cancer: clinical advances and resistance mechanisms.

Gastric cancer remains a major clinical challenge owing to its insidious onset and marked heterogeneity, which contribute to poor prognosis and limit the effectiveness of chemotherapy‑based systemic therapy. Antibody‑drug conjugates (ADCs) deliver potent cytotoxins to tumor cells with antigen specificity and have emerged as a therapeutic class that can enhance efficacy while reducing off‑target toxicity. Recent trials of ADCs targeting HER2, CLDN18.2, TROP2, CEACAM5/6, and HER3 demonstrate substantial therapeutic activity. Notably, the HER2‑directed agents trastuzumab deruxtecan and disitamab vedotin have improved survival and response in previously treated advanced disease. ADCs targeting CLDN18.2 and TROP2 have also yielded encouraging early results. Accumulating evidence from ongoing programs indicates movement into earlier lines of therapy in advanced gastric cancer, including evaluation in first‑line combination regimens. Broader clinical use has highlighted resistance mechanisms, including antigen loss or heterogeneity, impaired internalization and lysosomal processing, increased drug efflux, and an immunosuppressive tumor microenvironment that limits delivery. This review synthesizes clinical advances in ADC therapy for gastric cancer, delineates resistance biology, and evaluates strategies to overcome therapeutic resistance. Deeper mechanistic insight, biomarker‑guided patient selection, and continued innovation in targets, linkers, payloads, and rational combinations will be critical to overcome resistance and improve outcomes for patients with gastric cancer.