Table 2.

Methodological non‐negotiables for systematic reviews for the purposes of tumor classification

Rationale	Risks (if not considered in the review)
1. Transparency
Methods should be clearly stated and previously defined. Inclusion and exclusion criteria stated and applied. A review protocol should be written and made publicly available as an explicit statement of intended methods where deviations to these methods can be noted (with justifications). This ensures accountability by authors and facilitates replication of the review. Conflict of interests of the review team, as well as funding information, needs to be disclosed.	Methods may not be appropriate to ensure equitable representation of literature globally Unjustified deviations to planned methods remain unchallenged Undeclared conflicts of interest or researcher allegiance from authors may influence conclusions
2. Searching rigor
Searching two major bibliographic databases, (e.g., PubMed and Web of Science), minimizes the chance that a highly relevant study will be missed. While there are overlaps in medical bibliographic databases, indexing varies considerably. Therefore searching only one database means that retrieval of relevant literature is highly dependent on appropriateness/accuracy of the search strategy.	Reliance on one database capturing all relevant studies, reliance on all relevant studies being accurately indexed and reliance on a single search strategy being sufficient to capture all relevant literature Failure to identify all relevant literature
3. Double checking
Duplication of the data extraction and a proportion of the total study selection done by the primary author should be completed by a second reviewer for accuracy. Where multiple discrepancies are noted, further checking may be required for consistency.	Reliance on the accuracy and consistency of one author for all study selection and data extraction Bias in selection of studies Greater chance of erroneous study selection or data extraction
4. Risk of bias assessment
A methodological quality assessment tool for pathology reviews should be adapted, based on standardized risk of bias assessment tool. This helps review authors to assign more weight to findings from studies of higher quality or at lower risk of bias in interpretation.	No objective method of appraising studies for higher risk of bias Biases from primary studies are perpetuated in the review Bias in interpretation of studies may be applied by review authors