Passive smoking and risk of pancreatic cancer: an updated systematic review and meta-analysis

Background. Previous meta-analysis has demonstrated that no association was validated between passive smoking and pancreatic cancer. However, there is growing evidence on this issue recently. This study aimed to confirm this association. Methods. PubMed, Embase, Web of Science, and Cochrane Library databases were searched up to April 2024 for retrieval of full articles. Studies with the exposure of passive smoking and outcome of pancreatic cancer were eligible for the analysis. We generated pooled relative risks (RRs) and 95% confidence intervals (CIs) using DerSimonian-Laird random-effects models. Quality of evidence was assessed using the GRADE system. Results. Fourteen studies were included, with 5,560 pancreatic cancer patients. Passive smoking was associated with a moderate increased risk of pancreatic cancer (RR = 1.20, 95% CI: 1.11-1.30, p < 0.001). The results were consistent in both case-control (p=0.013) and cohort studies (p < 0.001) and in studies with high (p = 0.007) and moderate quality (p < 0.001). In subgroup analysis, the risk was significant for both current (RR=1.91, 95% CI: 1.45-2.51, p < 0.001) and non-current smokers (RR = 1.17, 95% CI: 1.01-1.36, p = 0.037), for exposure both in adulthood (RR = 1.18, 95% CI: 1.06-1.31, p = 0.002) and childhood (RR = 1.20, 95% CI: 1.08-1.34, p = 0.001). However, only regular or daily exposure (RR=1.28, 95% CI: 1.08-1.50, p = 0.003), rather than exposing occasionally, seldom or few times per week (p = 0.421), to passive smoking could increase the risk of pancreatic cancer. Conclusion. Passive smoking exposure confers a significant increased risk for pancreatic cancer. The risk was valid in both case-control and cohort, high and moderate quality studies, in current and non-current smokers, and for both childhood and adulthood exposure. Regular or daily exposure rather than exposing occasionally, seldom or few times per week could exert a detrimental effect on pancreatic cancer.