Sex/gender differences in the association between behavioural factors and cancers: an umbrella review of systematic reviews with quantitative synthesis

Many systematic reviews have summarized evidence on the association between behavioural factors and incident cancers. To date, there has been little synthesis of heterogeneity by sex/gender of this evidence.An umbrella review was conducted of systematic reviews with quantitative synthesis (meta-analysis, meta-regression) examining the exposures of body size; physical activity; wholegrains, vegetables, fruit and beans; "fast foods"; red and processed meat; sugar sweetened drinks; dietary supplements; alcohol; tobacco; and sun exposure with incident non-sex-specific cancers. A search of Ovid MEDLINE, Ovid Embase, and Cochrane library from database inception to May 2023 was conducted. We calculated the proportion of systematic reviews that provided quantitative sex/gender findings (e.g., subgroup analyses) and summarized findings narratively. Methodological quality was appraised with the AMSTAR-2 tool.From 13,227 records, 705 full-text systematic reviews were identified as meeting inclusion criteria. Of these, 361 (51.2%) reported quantitative sex/gender findings. The terms "sex" and "gender" were used interchangeably by 36.3% of the 361 systematic reviews and none reported findings for transgender, gender-diverse, or non-binary individuals. Overall, 98.6% (356/361) of systematic reviews were rated "critically low" with the AMSTAR-2 tool. Most of the 361 systematic reviews with quantitative sex/gender findings reported no statistically significant differences by sex/gender.This umbrella review found conflation of sex and gender in systematic reviews of behavioural factors and non-sex-specific cancers and a lack of research among non-cisgender individuals. The existing evidence base is of critically low quality and our findings of no sex/gender-specific trends must be interpreted with caution.