The prevalence of KRAS mutation in colorectal cancer patients in Iranian population: A systematic review and meta-analysis study

Colorectal cancer (CRC) is one of the most common cancers in the World that KRAS mutations are considered as a key step in the progression of CRC. This meta-analysis study aimed to evaluate the prevalence of KRAS mutations in CRC patients in Iran. Six online databases including PubMed, Science direct, Scopus, Web of science, Cochran Library, and Scientific Information Database (SID) were searched systematically up to January 2017. A random-effects meta-analysis was used to calculate the estimation of the prevalence of KRAS mutations in CRC patients by the event rate (ER) with 95% confidence interval (95%CI). Out of 82 articles identified from the search, eleven studies included and analyzed for meta-analysis study. The studies included 1814 CRC patients that mean age of the patients was 57.5 years. The pooled ER of the studies for estimation of the prevalence of KRAS mutation in CRC patients was 32.8% (95%CI=28.7-37.3%). The pooled ER of the studies for the prevalence of codon 12 mutation was 72.5% (95%CI=59.8-82.3%) and for codon 13 mutation was 20% (95%CI=14.6-26.7%). The results showed that the prevalence of KRAS mutation in Iran was different with more studies that therefore the geographical area and race can impact on the prevalence of KRAS mutation in CRC patients. Also, codon 12 had the most prevalence among mutant codons, followed by codon 13 that Gly to Asp and Gly to Val were the most mutations in codon 12. ! Biomed Res Ther 2017, 4(10): 1676-1692 !1676 DOI: 10.15419/bmrat.v4i10.374 ISSN: 2198-4093 www.bmrat.org


Introduction
Colorectal cancer (CRC) is the fourth most common cancer in men and the third most common in women (Amirifard et al., 2016). There are very few studies about KRAS mutations in CRC from developing countries such as Iran (Bishehsari et al., 2006). The latest data from the cancer patients' registry program showed that the age-standardized incidence rate had risen from 2.8 to 5.5 in 2009 and reached 9.2 in 2012 per 100,000 persons (Dolatkhah et al., 2016). KRAS is a proto-oncogene located on the short arm of chromosome 12, encodes the protein KRAS, a GTPase involved in cell division, differentiation and apoptosis (Dobre et al., 2015). The prevalence of KRAS mutation in CRC patients is 35-40 %, and the majority of these mutations occur in codon 12 and less frequently in codon 13 of KRAS gene (Rosty et al., 2013). Mutations activating the KRAS proto-oncogene are considered a key step in the progression from normal colorectal epithelium to carcinoma (Fearon and Vogelstein, 1990). Roughly 90% of the activating mutations, that are influential solitary amino acid replacement in the GTPase pocket that guide to a block of the activity of KRAS p21 protein, are recognized in codons 12 (GGT) and 13 (GGC) of exon 1 and almost 5% in codon 61 (CAA) situated in exon 2. The most regularly found kinds of mutations are G>A and G>T transitions (Palmirotta et al., 2009). This meta-analysis study aimed to indicate the prevalence of KRAS mutations in CRC patients in Iran.

Search Strategy
Six online databases including PubMed, Science direct, Scopus, Web of science, Cochran Library, and Scientific Information Database (SID) were searched systematically up to January 2017 with the terms of "KRAS" or "K-ras" and "colorectal" or "colon" or "rectum" or "rectal" in combination with "Iran".

Study selection
One author (E.S) searched the articles and then the second author (M.S) blinded to the first author that if there was any disagreement between two authors, both resolved the problems with two-way conversation. The third author (M.P) did the

Data Extraction
Name of the first author, year of publication, Province of the region, number of CRC patients, number of mutations, percentage of male (%), the mean age, number of mutant codons, and number of mutant amino acids of codon 12 were the relevant data extracted from every study.

Statistical analysis
A random-effects meta-analysis was used by Comprehensive Meta-Analysis software version 2.0 (CMA 2.0). The event rate (ER) with 95% confidence interval (95%CI) was calculated for estimation of the prevalence of KRAS mutations in CRC patients. Heterogeneity between estimates was assessed by the Q and I 2 statistic that for the Q statistic, heterogeneity was considered for P<0.1. P-value (2-sided) <0.05 was considered to be statistically significant in this meta-analysis study. Also, publication bias was assessed through funnel plot analysis with the Begg's and Egger's tests.

Results
From the initial 82 articles identified from the search, after excluding the studies, 18 studies were assessed for eligibility. Then, seven studies were excluded based on reasons. At last, eleven studies included and analyzed for metaanalysis study (Fig. 1).

Publication bias
Funnel plot of random effect of the studies for the prevalence of KRAS mutation in CRC patients has been shown in Figure 5. The Begg's and Egger's tests didn't show publication bias (P=0.102 and P=0.433, respectively).

Discussion
The meta-analysis study on eleven studies showed that the ER of KRAS mutation was 32.8% (95%CI: 28.7 to 37.3%) in CRC patients in Iran. KRAS mutation is one of the most common oncogenic changes in various types of human cancer (Amirifard et al., 2016). Mutation in codons 12, 13, and 61 of KRAS is common in CRC (Amirifard et al., 2016). Some studies in different parts of word reported the prevalence of KRAS mutation was 24% in the Middle East (Burt, 2000), 36% in Europa, (Ciardiello et al., 2011) 37.4% in Asian, 23% in Thailand, and 50% in Japan. In European countries, KRAS mutation was 30% in Italy, 49.3% in the UK, 31.6% in the USA, 28% in Australia, 23 to 28% in Africa, (Omidifar et al., 2015), 38% in France (Chretien et al., 2013) and 62.2% in Italy (Miglio et al., 2013). Therefore, the rate of KRAS mutation in the World was between 23 -50%. Three studies reported in Turkey checked 50, (Gorukmez et al., 2016) 172, (Selcukbiricik et al., 2013) and 53 (Ozen et al., 2013) mCRC patients that the prevalence of KRAS mutation was 30%, 44%, and 49.05%, respectively. Recent reports have shown that KRAS mutation in codon 12 is observed at frequencies of 12-30% and 35-50% among CRC patients in Asian and Western countries, respectively (Amirifard et al., 2016). In Romania, KRAS mutations in codon 12 accounted for 79.3% and codon 13 was 19.7% (Dobre et al., 2015). In Egyptian, KRAS mutations in codons 12 and 13 were present in 90% of cases with mutation (El Kader et al., 2013). One study in France (Chretien et al., 2013) reported KRAS mutations in 82.4% happened in codon 12 and 17.6% in codon 13. In sixty-one cases selected from the Greek population, the frequency of the mutation in the codon 12 was 28.3% (Symvoulakis et al., 2007). Mutation status in codon 12 and codon 13 were 62.2% and 21.4% (Miglio et al., 2013). The rate of codons 12 and 13 were 75% and 19%, respectively, that was near to the results of other studies.
In Egyptian, in codon 12, the most regularly found kinds of mutations were Gly to Asp (Dobre et al., 2015). In other study, the most common mutations were transitions of nucleotides Gly to Asp (28.7%) and Gly to Val (25%) (Miglio et al., 2013). The present meta-analysis study showed that Asp (47%) and Val (34%) were the most mutations in Iran that the results were similar.

Limitations
More studies were not sex-matched.
Some studies reported the prevalence just in metastatic CRC and rest of studies both metastatic and non-metastatic CRC.
The studies reported in different areas and races of Iran that geographical area and race can effect on the prevalence of mutations.
In a number of studies, except for codon 12 and 13, types of other different codons have been checked.

Conclusions
The meta-analysis showed that the prevalence of KRAS mutation in Iran was different with more studies that therefore the geographical area and race can impact on the prevalence of KRAS mutation in CRC patients. Also, Codon 12 had the most prevalence among mutant codons, followed by codon 13. At last, Gly to Asp and Gly to Val were the most mutations in codon 12.