طيف وتردد طفرات الجين K - ras عند المرضى العراقيين المصابين بسرطان القولون والمستقيم المفرق == Spectrum and Frequency of K - ras Mutations among Iraqi Patients with Sporadic Colorectal Cancer
Author name:
شيماء خالد شاكر احمد
Supervisor name:
بسام موسى صادق الموسوي
General topic:
Medicine
Specific topic:
Diseases - Genetics
Degree:
Master
University:
University of Baghdad - Faculty Of Medicine
Language:
English
University location:
Baghdad
First pages:
19T1333 - p.pdf
Abstract:
Colorectal cancer (CRC) is a serious health problem and is one of the most common cancers in the world. The majority of CRCs are sporadic; several genes have been implicated in colorectal carcinogenesis.Kirsten rat sarcoma viral oncogene homolog (K - ras) is a protooncogene and is one of the important genes responsible for sporadic colorectal carcinogenesis. It is involved in G protein - mediated signal transduction. It has a constitutive guanosine triphosphatase (GTPase) activity, which is lost when the gene is mutated. Analysis of K - ras mutation has important therapeutic impact being one of the most important predictors of resistance to targeted therapy using Epidermal Growth factor receptor (EGFR) tyrosine kinase inhibitors (cetuximab and panitumumab) in addition to its prognostic significance. Aim of study : To determine the frequency and spectrum of K - ras mutations among Iraqi patients with sporadic CRC. Patients, Materials and Methods : This is a retrospective study that included 35 surgically resected cases with sporadic CRC from the Gastroenterology and Hepatology Teaching Hospital / Medical City Complex - Baghdad during the period extending from January 1st, 2014 till December 31st, 2015. Patients’ demographic characteristics as well as tumor characteristics were studied. Samples of DNA were extracted from formalin - fixed paraffin embedded blocks (FFPE) using the QIAamp DNA FFPE Tissue Kit by QIAGEN / Germany. The specified DNA fragment was amplified by a conventional thermocycler (PCR) using specific biotinylated primers followed by hybridization of the amplification products to a test strip containing allele - specific oligonucleotide probes immobilized as an array of parallel lines. The bound biotinylated sequences are detected using streptavidin - alkaline phosphatase and color substrates according to the manufacturers’ instructions.Results : The age of the 35 enrolled cases ranged between (20 - 70) years with a mean (±SD) of 52.7±13.5 years and a median of 55 years; 27(77%) of them were ≥45 years of age and 8(23%) were <45 years of age. Out of the 35 enrolled patients 12 (34%) were males and 23(66%) were females; the male : female ratio was 1 : 2.The most common histological type was the non - mucinous adenocarcinoma constituting 30 (85.7%), with a moderately differentiated grade II histological pattern 29 (82.9%); stage III was the most common tumor stage 13 (37.1%) with predominance of left colonic tumors 20 (57%);15(42.9%) of CRC patients presented with positive regional lymph node involvement.K - ras mutations were detected in 13 (37%) patients; the remaining 22 (63%) show wild - type K - ras. Ten (71.4%) of these mutations were in codon 12 while 4(28.6%) were in codon 13. No mutation was detected in other codons (61,117,146).A total of 14 mutations were detected in the tumors of those 13 patients; 12/13 tumors had single mutations, and only 1/13 had double mutations (in codon 12 and codon 13 simultaneously).The most frequently encountered mutations were the G>T transversions 9 (64.4%). The most frequent mutation constituting 8 (57.2%) was GGT>TGT (GLY>CYS) at codon 12.There were no statistically significant associations of clinicopathological characteristics with K - ras mutation status.Conclusions : K - ras mutations rate lies within worldwide reports, and lie in the middle between Asian and European figures. Most CRC tumors carry codon 12 K - ras mutations and thus they have a risk of poorer prognosis and response to therapy. Gly12Cys and Gly13Asp predominate over other types of amino acid substitutions, and carry a poorer prognosis. PCR detection of K - ras mutations is preferable to IHC techniques especially so when using anti - EGFR for CRC treatment.
