In case of heterogeneity, meta-analysis was performed applying the random-effects model. In addition, an I2 value of less than 25% was defined to represent low heterogeneity, a value between 25 and 50% was defined as moderate heterogeneity, and a value of >50% was defined as high heterogeneity.36 Subgroup analyses, which considered more homogeneous

studies, were performed to identify subsets of patients more likely to benefit from the treatment and to assess the efficacy of different studies. To determine the extent to which the combined risk estimate might be affected by individual studies, sensitivity analysis was RG7204 performed by consecutively omitting every study from the meta-analysis (leave-one-out procedure). Funnel plots were used to screen for publication bias. Meta-analysis was conducted by Review Manager (RevMan) Meta-analysis software,

v. 5.1.6. The 95% CIs were calculated as estimates of precision for OR. The statistical tests were two-sided, and P < 0.05 was considered statistically significant. Detailed analytical methods can be found in the Supporting Algorithms for Data Combination in the Meta-analysis. Table 1 lists the characteristics of the included studies and details of the enrolled participants. Figure 1 illustrates the study screening and selection process. A total of 2,880 patients (simultaneous resection 1,015, delayed resection 1,865) from 17 see more studies were included. Synchronous metastases were defined as liver metastases diagnosed before colorectal resection or at the time of surgery, and patients scheduled for a so-called “two-stage hepatectomy” procedure (two sequential hepatectomies for bilateral metastases unresectable by a single resection) were excluded from the meta-analysis. Most studies were from Western Europe and North America in single-centers analyzed retrospectively and the

number of patients per study ranged from 36 to 610 (multicenter study for Reddy et al.).27, 39 Preoperative chemotherapy status was reported in five studies.27, 40, 42, 47, 49 Moreover, we observed that patients with restricted metastatic disease were more likely to undergo simultaneous resections, whereas extended MCE公司 and anatomical difficult resections were rather performed as staged procedures. Distributions of risk (Severity) characteristics for the included patients from each observational study are detailed in Supporting Table 1. The agreement between two reviewers for study selection was 0.94 and for quality assessment of trials was 0.89. We evaluated the risk of bias in the 17 observational studies by modification of the Newcastle-Ottawa scale (Table 2).32 Detailed descriptions of follow-up were available in most studies.