Abstract
BACKGROUND: Kirsten Rat Sarcoma (KRAS) copy number amplification has emerged as an oncogenic driver in colorectal cancer (CRC), in addition to KRAS mutation. However, its clinical significance remains poorly understood. Notably, CRC patients with wild-type KRAS but harboring KRAS amplification have shown resistance to anti-EGFR therapy, representing an unmet clinical need. METHODS: In this study, we comprehensively investigated the impact of KRAS amplification-alone and in conjunction with mutation-on clinicopathological characteristics, immune infiltration, and therapeutic response. KRAS copy number variation (CNV) was classified into amplification and non-amplification groups. KRAS mutational status was determined as wild-type (WT) or mutant (MUT) using qPCR and Sanger sequencing. CD8⁺ T lymphocyte infiltration was evaluated by immunohistochemistry in resected CRC specimens. Clinical, immune, and survival data were analyzed in association with KRAS status. RNA-seq was performed to identify differentially expressed genes (DEGs) and enriched pathways. Patient-derived xenograft (PDX) models were used to assess responses to targeted therapies. RESULTS: We found that KRAS amplification was more frequent in WT KRAS CRC (21.4%) than in MUT KRAS CRC (6.5%). In the WT subgroup, KRAS amplification was associated with poor prognosis and increased KRAS protein expression and downstream pathway activation. In contrast, amplification had little effect in mutant KRAS tumors. KRAS copy number was inversely correlated with CD8⁺ T cell infiltration, suggesting a role in immune evasion. Importantly, low CD8⁺ T cell density combined with KRAS amplification predicted adverse outcomes. Therapeutically, KRAS-amplified PDX models were resistant to anti-EGFR treatment. However, combined MEK and CDK4/6 inhibition overcame this resistance. CONCLUSIONS: KRAS amplification constitutes a distinct oncogenic driver in CRC and a potential biomarker for therapeutic stratification. Our findings support the clinical rationale for dual MEK and CDK4/6 inhibition in KRAS-amplified CRC and highlight the need for biomarker-guided clinical trials to optimize treatment strategies in this subset of patients.