Fig. 1

A flow diagram demonstrating the study selection process. Out of 397 identified records, 111 were chosen for systematic review and 85 for overall survival meta-analysis. Duplicate exclusion refers to the process of asserting that each paper is only represented once within our set of records. Initially, 111 records with titles seemingly irrelevant to the objectives of our study were excluded, following which another 81 records were excluded after reading through the remaining 192 papers, for the reasons identified within the diagram. This process led to the identification of 111 papers eligible for systematic review. We then applied our meta-analysis eligibility criteria to these papers, on the basis of which 26 were excluded, for the reasons identified in the diagram. This process led to the identification of 85 papers eligible for meta-analysis