A Clinical and Molecular Comparative Analysis of KRAS Exon 2 and KRAS Non-Exon 2 Mutated Colorectal Cancer

Mutations in the KRAS oncogene occur in approximately 40% of colorectal cancers, predominantly within exon 2. Non-exon 2 mutations are less common and remain poorly characterized in terms of their clinical and biological significance. Systemic inflammatory markers are well-established prognostic indicators in colorectal cancer, yet whether their prognostic value differs across KRAS mutation subtypes has yet to be defined. We aimed to characterize and compare the clinicopathological and inflammatory profiles of patients with exon 2 versus non-exon 2 KRAS-mutated colorectal cancer and evaluate their prognostic implications.

This retrospective cohort study analyzed 272 patients with microsatellite stable metastatic colorectal cancer with KRAS mutations, comprising 236 exon 2 and 36 non-exon 2 cases. Clinical, molecular, and laboratory data, including baseline systemic inflammatory markers, were extracted from electronic medical records. Survival outcomes and the prognostic impact of these variables were evaluated with Kaplan-Meier curves and univariable and multivariable Cox proportional hazards regression analyses.

Non-exon 2 mutations were significantly more frequent in female patients (64% vs. 45%, p = 0.048) and in left-sided primary tumors (83% vs. 64%, p = 0.035). Median overall survival was 45.7 months for the non-exon 2 group compared to 32.4 months for the exon 2 cohort; KRAS mutation subtype was not significantly associated with overall survival on univariable or multivariable analysis (univariable HR 1.36, 95% CI 0.85-2.16, p = 0.2; multivariable HR 1.376, 95% CI 0.794-2.383, p = 0.255). Systemic inflammation demonstrated distinct prognostic value, with elevated white blood cells, absolute neutrophil count, platelets, neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and low albumin levels demonstrating association with worse overall survival in the exon 2 cohort. Conversely, only an elevated neutrophil-to-lymphocyte ratio predicted worse survival in the non-exon 2 group.

KRAS exon 2 and non-exon 2 mutated metastatic colorectal cancers exhibit distinct clinical and inflammatory characteristics. Systemic inflammation exerts a significantly greater prognostic impact in exon 2 disease. As the therapeutic landscape for KRAS-mutated CRC continues to evolve, these findings hold promise for informing KRAS mutation-specific approaches to patient stratification and treatment planning.