Primary tumor resection in patients with unresectable colorectal cancer with synchronous metastases could improve the activity of poly-chemotherapy: A trial-level meta-analysis

•Primary tumor resection (PTR) is less and less used in metastatic colorectal cancer.•Eleven studies reported progression-free survival (PFS) after PTR and chemotherapy.•The PFS after PTR + chemotherapy was longer then after chemotherapy alone.•Female sex, liver metastases and poly-chemotherapy were associated with the effect size.