Objective To explore the value of KRAS mutation predicting prognosis of patients with colorectal liver-only metastasis after hepatectomy.Methods The retrospective case-control study was conducted.The clinicopathological data of 79 patients with colorectal liver-only metastasis who underwent hepatectomy in the Sun Yat-sen University Cancer Center between October 2010 and October 2016 were collected.KRAS mutation in colorectal cancer tissue was detected by fluorescent quantitative polymerase chain reaction (PCR) and laser flight mass spectrometer.Observation indicators:(1) KRAS mutation;(2) relationship between KRAS mutation and clinicopathological factors of patients with colorectal liver-only metastasis;(3) follow-up and survival situations.Follow-up using outpatient examination and telephone interview was performed to detect recurrence-free survival and overall survival up to June 30,2017.The relationship between KRAS mutation and clinicopathological factors of patients with colorectal liver-only metastasis was analyzed by the chi-square test or Fisher exact probability.The survival curve and time were respectively drawn and calculated by the Kaplan-Meier method,and COX regression model was used for survival analysis.Results (1) KRAS mutation:79 patients received KRAS gene detection of surgical tumor tissues,including 54 in wide-type mutation and 25 in mutant-type mutation.Of 25 patients in mutant-type mutation,mutation at codon 12 of KRAS exon 2 was in 21 patients,and GGT＞GAT (G12D),GGT＞GTT (G12V),GGT＞TGT (G12C),GGT＞GCT (G12A) and GGT＞CGT (G12R) of mutation types were respectively detected in 13,4,2,1 and 1 patients;mutation at codon 13 of KRAS exon 2 was in 3 patients,with a mutation type of GGC＞GAC (G13D);mutation at codon 61 of KRAS exon 3 was in 1 patient,with a mutation type of CAA＞CAT (Q61H).(2) Relationship between KRAS mutation and clinicopathological factors of patients with colorectal liver-only metastasis:primary tumor located in right and left hemicolon were detected in 11,14 patients with mutant-type mutation and 7,47 patients with wide-type mutation,respectively,with a statistically significant difference (x2=9.357,P＜0.05).(3) Follow-up and survival situations:79 patients were followed up for 2.0-71.0 months,with a median time of 29.0 months.Median recurrence-free survival time and median overall survival time were respectively 11.3 months,43.5 months in patients with mutant-type mutation and 9.9 months,44.3 months in patients with wide-type mutation,respectively,with no statistically significant difference in recurrence-free and overall survivals [hazard ratio (HR)=1.255,1.108,95％ confidence interval (CI):0.741-2.126,0.521-2.355,P＞0.05].Further analysis:of patients with low clinical risk score (CRS) of Memorial Sloan Caitlin Cancer Center (MSKCC),median recurrence-free survival time was 11.3 months in 17 patients with mutant-type mutation and 23.5 months in 26 patients with wide-type mutation,with a statistically significant difference in recurrence-free survival of patients (HR=2.082,95％CI:1.006-4.307,P＜0.05).The median overall survival time was 44.6 months in 17 patients with mutant-type mutation and 49.0 months in 26 patients with wide-type mutation,with no statistically significant difference in overall survival of patients (HR =1.165,95％CI:0.413-3.282,P＞0.05).Of patients with high CRS of MSKCC,median recurrence-free survival time and median overall survival time were respectively 5.6 months,28.7 months in 7 patients with mutant-type mutation and 4.5 months,36.7 months in 24 patients with wide-type mutation,with no statistically significant difference in recurrence-free and overall survivals (HR=0.402,1.197,95％CI:0.284-1.656,0.371-3.866,P＞0.05).Conclusions KRAS mutation is often detected in patients with right colon cancer.Recurrence-free survival time is obviously reduced in patients with KRAS mutation and low CRS of MSKCC.