Objective: Mutation in KRAS gene is one of the most common genetic changes among patients with colorectal cancer (CRC), which is observed in 30-45% of cases. This study aims to estimate the prevalence of this mutation among patients with primary or metastatic CRC.

Patients and Methods: Eligible studies were identified during a comprehensive electronic search, applying inclusion/exclusion criteria and quality assessment. Stata version 11 software was used for data analysis. The heterogeneity between the results of the primary studies was assessed using Cochrane and I-square indices. Random effect model was applied for combining the primary estimates. Point and pooled estimates (with 95% confidence intervals) were presented by forest plots. Investigating the factors associated with heterogeneity was carried out using meta-regression models. The publication bias was traced by Egger test.

Results: Combining the results of 164 eligible studies, the total prevalence of KRAS gene mutation among primary tumor samples was estimated as of 33.14% (95% confidence interval: 30.08- 36.20). The corresponding figure for metastatic cancer was estimated as of 36.20 % (95% confidence interval: 33.96- 38.44). Prevalence of this mutation among patients with primary CRC in EMRO, EURO, PAHO, SEARO and WAPRO was 30.23%, 35.12%, 31.83%, 33.17% and 32.64%, respectively. Corresponding rates for mutation among metastatic cases were 42.20%, 38.46%, 36.06%, 42.80%, 33.05%, respectively. In addition, the total prevalence of KRAS gene mutation in codons 12 and 13 was estimated as 76.69% and 28.49%, respectively.

Conclusions: More than one-third of patients with CRC carried KRAS gene mutation particularly in the metastatic tumors. The rate of mutation was the same in different WHO regions.