Abstract

Background: This systematic review and meta-analysis was conducted on the most relevant studies to determine any relationship between opium use and upper gastrointestinal (UGI) cancers. Methods: A comprehensive search was performed on several electronic databases, i.e. MEDLINE, PubMed, EMBASE, Scopus, Web of Science (ISI), Magiran, and SID, looking for studies that examined the association between opium use and UGI cancers up to August 2020. Q-tests, as well as I2 statistics, were employed to assess the inter-study heterogeneity. Moreover, the random-effects model was utilised to obtain estimates of the pooled crude and adjusted odds ratios (ORs) with their 95 confidence intervals (95 CIs). Results: Of 1,378 records, thirteen articles comprised 3,530 UGI cancer cases and 254,219 controls. The meta-analyses obtained from the random-effects model indicated that opium use was associated with an increased risk of UGI cancers, with a crude OR of 1.98 (95 CI: 1.67, 2.35) and an adjusted OR 1.76 (95 CI: 1.41, 2.20). Given the significant heterogeneity value observed in the pooled crude ORs (I2: 48.39 with P= 0.011), subgroup analyses showed that the pooled effect size remained statistically significant in the different strata, except in the strata stratified by type of cancers. Moreover, the findings of meta-regression analyses indicated the date of publication (beta=-0.02, P= 0.014) and the total sample size (beta=-0.00, P=0.034) might account for the inter-study heterogeneity. Likewise, sensitivity analysis indicated that none of the studies impacted the robustness of the pooled crude ORs. Conclusions: We found a significant association between opium use and developing UGI tract cancers, especially in oesophageal cancer.