Background: KRAS mutation occurs in 35%-40% of colorectal cancer (CRC). The aim of our study was to evaluate the pathological and molecular features of specific KRAS mutated colorectal carcinomas. KRAS and BRAF (V600E) mutation tests were performed in 762 primary tumors from a consecutive cohort study of Chinese CRC patients.
Methods: DNA mismatch repair (MMR) status was determined by immunohistochemistry (IHC) staining. Assessment of KRAS and BRAF V600E mutational status was performed using a multiplex allele-specific PCR-based assay.
Results: Mutations of KRAS (34.8%) and BRAF (V600E) (3.1%) were nearly mutually exclusive. Both KRAS- and BRAF- mutated tumors were more likely to be located at proximal colon than wild-type (WT) carcinomas. KRAS-mutated carcinomas were more frequently observed in female patients (47.5% vs 37.1%, p = 0.005) and mucinous differentiation (34.7% vs 24.8%, p = 0.004), but have no difference between lymph node (LN) metastases and among pTNM stages. Whereas, BRAF-mutated carcinomas more frequently demonstrated histologic features such as proximal location (60.9% vs 20.9%, p = 0.001), low-grade histology (43.5% vs 18.0%, p = 0.005), mucinous differentiation (69.6% vs 25.9%, p = 0.001) and deficient MMR (dMMR) (21.7% vs 7.6%, p = 0.03). In particular, KRAS codon 12 mutated carcinomas had increased lymph node metastasis (odds ratio [OR] = 1.31; 95% confidence interval [CI] = 1.04 to 1.65; P = 0.02) and were more likely in higher disease stage (III-IV) than that of WT carcinomas (OR = 1.30; 95% CI = 1.03 to 1.64; P = 0.03). However, there were no significant differences in lymph node metastasis and disease stage between KRAS codon 13 mutated carcinoma and WT carcinoma patients.
Conclusions: In summary, KRAS codon 12 mutation, but not codon 13 mutation, is associated with lymph node metastasis and higher tumor stages.