Distinct Molecular and Prognostic Profiles of Left‐ and Right‐Sided Colorectal Cancer Revealed by NGS Analysis: The Role of SMAD4 and SETD2 Mutations

Background Colorectal cancer (CRC) isthe third most common cancer and the second leading cause of cancer‐relateddeath worldwide. Its genetic heterogeneity complicates treatment. This studyaimed to compare clinicopathological, molecular, and prognostic factors betweenleft‐sided (LCC) and right‐sided (RCC) CRC. Methods We retrospectively analyzed 48 CRCpatients who received next‐generation sequencing (NGS) of tumor tissue andmatched leukocytes using a 425‐gene panel. Clinicopathological, molecular, andprognostic factors were compared between LCC and RCC. Results RCC exhibited a higher frequencyof BRAF mutations (33.3% vs. 7.1%, p = 0.042) and more frequent alterations in PI3K ( p = 0.033), homology‐dependent recombination (HDR, p = 0.018), and mismatch repair (MMR, p = 0.002) pathways than LCC. Multivariate analysis identified SMAD4 mutation as an independentpredictor of worse overall survival (OS) (HR = 3.88, 95% CI 1.05–14.29, p = 0.042), which was confirmed in an external cohort of 1796 CRCpatients. In subgroup analyses, SETD2 mutationswere associated with poor prognosis in LCC (HR = 2.20, 95% CI 0.80–6.06, p = 0.026), while ARID1A ( p = 0.040) and PRDM1 ( p = 0.021) mutations correlated with shorter progression‐free survival in RCC. Patients harboring both SMAD4 and SETD2 mutationshad the shortest OS (median: 17.7 months, p < 0.0001). Conclusions These findings reveal criticalmolecular and prognostic differences between LCC and RCC and highlight SMAD4 and SETD2 asimportant prognostic biomarkers, suggesting the potential value of location‐and mutation‐guided precision therapies in CRC.