The Egger's regression test showed that there was no publication bias in the literature on BMI and kidney cancer risk in obesity group (P = .671) and dose-response group (P = .265). For the document on BMI and kidney cancer risk in the overweight group, the Egger's test showed the probability of publication bias (P = .031) (Fig. 6). In view of this, we undertook the trim and fill analysis and the result was unchanged, indicating that the effect of publication bias could be omitted.
In a sensitivity analysis in which one study at a time was removed and the rest analyzed, the pooled RRs ranged from 1.31 to 1.36 for overweight, from 1.67 to 1.77 for obesity and from 1.37 to 1.40 for dose-response analysis, which demonstrated that the pooled estimates were steady.
Advantages of our study were the inclusion of more comprehensive cohort studies, a large number of participants and cases, and the evaluation of the possibility of potential nonlinear relationships. In addition, our study excluded an original cohort study included in the previous meta-analysis because the original study reported the mortality of kidney cancer, which made our results more authentic and more in line with the study design. Although this meta-analysis included more cohort studies than previous studies, it also has several potential limitations. Firstly, overweight/obesity is closed to unhealthy diet, as we all know, which is also related to kidney cancer, but diet habit was only adjusted in very few included studies, which made the subgroup analysis more difficult to interpret. Meanwhile, some unknown confounding factors that may affect the risk of kidney cancer had not been adjusted in most original studies, which may make the real association between BMI levels and kidney cancer risk estimated. Secondly, it was reported that people with visceral obesity were more likely to have fatty liver than those without visceral obesity, and it was also found that the liver lipid accumulation was related to kidney cancer. Unfortunately, our study only explored the relationship between BMI and kidney cancer risk due to the absence of information of visceral obesity in the original studies. Thirdly, it is impossible to completely exclude the potential publication bias because our meta-analysis only included the published studies. However, some studies with invalid results tend not to be published. Interestingly, the trim and fill analysis showed that publication bias could be negligible.
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