Data extraction and quality assessment of included studies
After selection of eligible studies, data extraction process was carried out by two authors (CA and NV) independently and was cross-checked at the end to remove any errors. General characteristics of included studies e.g. author name with publication year, country, study design, sample size, age, gender, chemotherapy regimen, dose and schedule of irinotecan, genotyping method etc. and clinical outcomes data e.g. number of events with irinotecan driven neutropenia/diarrhea corresponds to each genotype group were extracted after reading the full texts in depth. Any disagreements were discussed until consensus between the 2 reviewers could be reached.
The quality of included studies was assessed based on the Newcastle Ottawa Scale (NOS) guidelines. In this scale, quality assessment score ranges from ‘0’ to ‘9’ against ‘9’ criteria set in NOS in which each criterion was given a star (*) corresponds to score ‘1’. Studies were considered high quality if the NOS score was ≥6 and studies were moderate and low quality if the scores were ‘4–5’ and ‘0–3’, respectively [42, 43].