Molecular Diversity and Characteristics of KRAS Mutations in Colorectal Cancers

Abstract

Background: KRAS oncogene is involved in colorectal carcinogenesis in 22 to 45% of cases. KRAS mutations can render Epidermal Growth Factor Receptor (EGFR) inhibitors ineffective. The present study is aimed to determine the molecular diversity, frequency, and characteristics of KRAS mutations in metastatic Colorectal Cancer (mCRC). The gene KRAS contains 4 coding exons and 1 non-coding exon, of which exon 2 has the highest mutation rate, which is directly associated with the occurrence of poor prognosis and drug resistance. Codon 12, 13, 61 are common KRAS mutations. The most prevalent KRAS mutation observed was codon 12-G12D mutation where Glycine is changed to Aspartic acid. Materials and Methods: A retrospective study was conducted on both in-situ and metastatic colorectal cancers that were registered for KRAS gene mutation testing in Department of Molecular Pathology and Genomics, Kokilaben Dhirubhai Ambani Hospital & Medical Research Institute, from January 2016 to January 2022. KRAS mutations studies were carried out in primary and metastatic 87 patients of colorectal cancers. The samples contained 37 women aged 25-80 years and 50 men aged 29-77 years. Formalin fixed and paraffin embedded tissue samples were evaluated using Sanger sequencing and statistical analysis was carried out. Results: KRAS mutations were demonstrated in 26 cases of 87 patients (29.88%). Of the 26 cases, the substitution nucleotide variations as point mutations were as follows: Codon 12-18 cases (69%), codon 13-4 cases (15%), codon 61-2 cases (8%), codon 146-1 case (4%), and codon 10-1 case (4%). The Codon 12 mutations were detected as follows: G12D-9 cases (50%), G12V-3 cases (17%), G12A-3 cases (17%), G12S-2 cases (11%), G12C-1 case (5%); Codon 13 showed all 4 mutations (4%) in G13D. KRAS mutations were found to be more frequent in elderly age group. Most m-KRAS tumors were located in sigmoid colon and rectum (left sided/distal colon), although, the mutations were spread across including ascending colon (right sided/proximal colon) and rarely in jejunum too. The TNM stage showed majority (50%) of KRAS mutations in stage IV, and 20% of cases in stage II and III each. Conclusion: In this series, 29% of colorectal cancer tissue samples had KRAS mutations. Their frequency and distribution showed majority mutations on left sided/distal colon, elderly population, more common in females and presented at an advanced stage. There was no clinicopathological significance to histomorphology. Understanding KRAS mutations in different aspects can give a better comprehensive understanding of KRAS associated CRCs.