Genomic landscape and clinical characteristics of <i>ERBB2/HER2</i> -mutated colorectal cancers

Abstract Background Molecular underpinnings and clinical characteristics of ERBB2/HER2-mutated colorectal cancers (CRCs) remain poorly understood. We aimed to comprehensively characterize the genomic landscape and clinical features of ERBB2/HER2-mutated CRC and to compare them with those of ERBB2/HER2-amplified CRC. Patients and Methods We analyzed cBioPortal data from 4,348 CRC patients with available ERBB2/HER2 profiling. Clinicodemographic features, microsatellite instability (MSI), tumor mutational burden, and alterations in 94 cancer-associated genes were evaluated using chi-square/Fisher's exact test, Kruskal-Wallis test, and hierarchical clustering. Results ERBB2/HER2 putative driver mutations were identified in 95 patients (2.2%), amplifications in 87 (2.0%), and wild-type status in 4,166 (95.8%). In the overall cohort, ERBB2/HER2-mutated tumors demonstrated significant KRAS enrichment (50.5%) compared to wild-type (37.7%; p = 0.014) and amplified tumors (18.4%; p &amp;lt; 0.001), alongside MSI enrichment (37.2% vs. 1.6%; p &amp;lt; 0.001), elevated tumor mutational burden, and right-sided predominance. ERBB2/HER2-mutated tumors also showed broad driver co-alterations largely reflecting their MSI background. In contrast, ERBB2/HER2-amplified tumors exhibited left-sided predominance, with microsatellite stable (MSS)-restricted analyses revealing selective mutual exclusivity with KRAS (Log₂ OR = −1.58; q = 0.019) and TP53 co-occurrence (Log₂ OR = 2.04; q = 0.019). Hierarchical clustering confirmed that mutated and amplified tumors consistently occupy separate clusters across anatomical sites. Conclusion ERBB2/HER2 mutations and amplifications represent molecularly and clinically distinct subgroups. ERBB2/HER2-mutated tumors are characterized by an MSI-enriched, hypermutated background with frequent concurrent KRAS alterations, whereas amplified tumors exhibit selective KRAS mutual exclusivity and TP53 co-occurrence. These exploratory findings support alteration-specific therapeutic strategies in CRC.