An antibody-drug conjugate (ADC) composed of a monoclonal antibody directed against the tumor-associated antigen (TAA) Claudin18.2 (CLDN18.2; A2 isoform of claudin-18) conjugated to an as of yet undisclosed cytotoxic agent, with potential antineoplastic activity. Upon administration, anti-CLDN18.2 ADC IBI343 specifically targets and binds to CLDN18.2 expressed on tumor cells. Upon internalization, the cytotoxic agent induces apoptosis in CLDN18.2-expressing tumor cells through an as of yet unidentified mechanism of action (MoA). CLDN18.2, a tight junction protein and stomach-specific isoform of claudin-18, is expressed on a variety of tumor cells. Its expression in healthy tissues is strictly confined to short-lived differentiated epithelial cells of the gastric mucosa.