Metanalyses on metformin's role in pancreatic cancer suffer from severe bias and low data quality - An umbrella review.

AIMS: Discrepancies in the preclinical evidence, retrospective studies, and randomized trials evaluating metformin's role in pancreatic cancer are difficult to disentangle. We aimed to critically and systematically examine the quality and sources of heterogeneity between meta-analyses investigating the association between metformin intake and the prognosis of patients with pancreatic cancer.

MATERIALS AND METHODS: We performed a literature search on PubMed, MEDLINE, Embase, and Scopus on October 31, 2021 to identify meta-analyses investigating the impact of metformin treatment on the prognosis of patients with pancreatic cancer. Meta-analyses quality was assessed using according to the AMSTAR 2 criteria. We assessed bias in individual studies included in the meta-analyses, with particular attention to immortal time bias and quality of reporting.

RESULTS: Eleven meta-analyses describing 24 individual studies were included. All meta-analyses were rated low (n = 5) or critically low (n = 6) quality. Only 4 followed PRISMA reporting guidelines and only in 5 presented data were sufficient to replicate the analyses. Most meta-analyses combined results from clinical trials and retrospective studies (n = 6); patients with different cancer stages (resectable vs advanced) and from studies with different control group definitions. Immortal time bias was present and not accounted for in most (65.2%) of the individual retrospective studies; almost all (n = 9) meta-analyses failed to identify and correct for this source of bias.

CONCLUSIONS: Meta-analyses describing the association of metformin use in patients with pancreatic cancer are plagued by various types of bias inherent in retrospective studies. The quality of evidence linking metformin to decreased pancreatic cancer mortality is generally low.