Search Strategy and selection criteria

We performed a systematic search of published literature by primary malignancy from September 2020 to February 2021 in three databases: MEDLINE, EMBASE, and ClinicalTrials.gov. We also reviewed abstracts from major conference proceedings. To be included in this meta-analysis the study had to provide overall survival outcomes data in the form of hazard ratios (HR) for patients with liver metastases compared to other sites of disease. In the event that a hazard ratio was not reported median survival times were used as an approximation of hazard. All study types, including clinical trials, prospective and retrospective/observational studies, were included in the search. Three reviewers (JW, MG, VM) independently searched the databases using predefined MESH or EMTree search terms. Pubmed MESH terms used included: “Liver Neoplasms/Secondary” AND “Prognosis” AND “[primary malignancy]” and Embase EMTree terms used included: “cancer prognosis/exp” AND “[primary malignancy].” For specific primary malignancy terms used see Table 1. Using these terms, 14,788 studies were identified. Following de-duplication and initial title and abstract screen for the appropriate search terms, 1,240 studies were included. Of these, 472 studies contained overall survival outcome measures on patients with liver metastases and were included for full text analysis. Three reviewers (JW, VM, ZC) independently assessed if studies met the predetermined criteria and a fourth reviewer, MG, was consulted in case of disagreement. All discrepancies were discussed and resolved with the consensus of all investigators. Three reviewers (JW, VM, ZC) extracted data from each study.

Search Terms