ERBB2 and neoplasm: This finding is consistent with both the exceptionally low co-occurrence rate (0.7%) reported in KEYNOTE-811 (4) and the fundamentally distinct molecular profiles of these tumor subtypes: while HER2-amplified tumors typically exhibit chromosomal instability with low mutational burden, MSI-H tumors display mismatch repair deficiency-driven hypermutability without recurrent amplifications (27).