This study also evaluated the concordance of CLDN18.2 positivity (defined as ≥ 75% of tumor cells demonstrating moderate-to-strong membranous CLDN18 staining) or any CLDN18 staining (defined as ≥ 1% of tumor cells demonstrating moderate-to-strong membranous CLDN18 staining) in a subset of pair-matched samples consisting of archival tumor samples (collected any time before treatment) and baseline tumor samples (collected within 3 months before first study treatment) from the ILUSTRO study (cohorts 1A and 2) and the phase 1 study of Japanese patients. The gene discussed is CLDN18; the disease is neoplasm.