Literature search
The present umbrella review of systematic reviews and meta-analyses was
based on a predefined research protocol. It was conducted in accordance
with the preferred reporting items for overviews of systematic reviews
(PRIO; Supplementary Table 1) .
We searched PubMed and Scopus databases until April 23 2020 for
systematic reviews and meta-analyses on the association of any
environmental risk factor and any type of childhood cancer employing a
predefined search algorithm (Supplementary Material). No language or
other restriction criteria were applied. Two independent investigators
(MK and GM) examined the titles, abstracts and full texts of the
shortlisted meta-analyses and discrepancies were resolved by consensus.
We further hand searched the references of the retrieved systematic
reviews and meta-analyses for systematic reviews/meta-analyses
potentially missed by the initial electronic search and unpublished
data.