Genetic Variations of Selected Genes Using Target Deep Sequencing in Colorectal Cancer Patients

Abstract

Background: Colorectal carcinoma (CRC) is a burden problem in a developing country like Egypt since patients are usually admitted in late stage with bad prognosis and short overall survival. Because of genetic predisposition of CRC and introduction of advanced molecular techniques, efforts are directed to screen for potential pathogenic or disease-causing variants in CRC patients Methods: DNA was isolated from formalin fixed paraffin embedded tissue sections collected from 24 CRC confirmed diagnosed patients. TruSight CRC panel (Illumina) was used for detection of different variants in 15 genes. The generated reads were obtained from Illumina Miseq were clustered into single nucleotide polymorphism (SNPs) and small insertions/deletions (Indels). Further pathogenic variants with somatic and germline mutations were identified according to the recommended criteria. Some CRC patients were subjected to anti-EGFR target therapy. Results: Most of the variants were detected in TP53 gene 140 variants (65%); 105 short deletions none of them was pathogenic, 29 missense mutations and 6 SNPs at splicing sites. Next, ERBB2 has got 17 variants (8.8%) (missense and splicing), 8 of them were damaging disease causing variants. Besides, 16 pathogenic variants were identified in 12 patients (6 in TP53 and 7 in KRAS). Some pathogenic variants were not reported before in CRC e.g. TP53 C>A, rs121912654, Val157Phe. Additionally, patients carried different KRAS wild mutations showed variable response to anti-EGFR target therapy. Conclusion: The most affected pathway in CRC was TP53 pathway followed by ERBB2, NRAS, KRAS and PIK3CA genes. Variable response to target therapy suggested dependence on the type of pathogenic variant identified, also a possible role of ERBB2 which had a significant variant frequency.