Baseline imbalance in studies included in the meta-analysis.

Y: significant imbalance of baseline; N: no significant imbalance of baseline; NA: data not available.Location was compared as: (right-sided vs. left-sided vs. rectum)a or (colon vs. rectum)b. When compared as (right-sided vs. left-sided vs. rectum)a, the transverse colon was included in the right-sided, the sigmoid colon was included in the left-sided.T stage was compared as T1+T2 vs. T3+T4.N stage was compared as N0 vs. N+.Number of metastases was compared as: (single vs. multiple)c or (≤3 vs. >3)d or (mean ± SD)e or others with no superscript.Maximum diameter of metastases was compared as: (≤5 cm vs. >5 cm)f or (mean ± SD)g or others with no superscript.Major hepatectomy was defined as resection with ≥3 segments.Preoperative chemotherapy included chemotherapy before both primary resection and hepatectomy.The study Vassiliou 2007 enrolled only patients with ≤3 liver metastases.