The meta-analysis is a powerful statistical tool to estimate the incidence and risk of those uncommon serious drug-related toxicities and this approach has been utilized to IMR-1 demonstrate an increased risk in treatment related mortality with bevacizumab and VEGFR-TKIs in previous researches. To the best of our knowledge, this is the first meta-analysis to investigate the incidence and risk of FAE associated with the mTOR inhibitors everolimus and temsirolimus. Our meta-analysis included 3322 patients from 12 trials demonstrates the overall incidence rate of FAEs is 1.8%, and there is a significant threetimes increased risk of death with these agents. However, a nonsignificantly increased risk of mTOR inhibitor associated FAEs is observed in sub-group analysis according to the mTOR inhibitors, tumor types and controlled therapy, for which we suggest several possible explanations: the small number of events recorded; underreporting of rare adverse events; the fact that clinical trials are usually not designed specifically to address toxic events; and the small number of randomized controlled trials included. As mTOR inhibitors find more clinical applications and are used to treat a more heterogeneous patient population than those found in clinical trials, efforts are still needed to limit the risk of FAEs. Patients receiving mTOR inhibitors should be carefully monitored for the evidence of infection, especially patients with underlying known chronic lung disease or risk factors of infection. What’s more, as the use of mTOR inhibitors could cause noninfectious pneumonitis, which is characterized by non-infectious, non-malignant, and non-specific inflammatory infiltrates. Therefore, high-resolution computed tomography scans might be performed for patients present with cough and/or dyspnoea and/ or hypoxemia, and/or fever when receiving mTOR inhibitors. In addition, previous researches have demonstrated that pneumovax is effective in preventing both influenza and pneumococcal infection, thus it might be a potential effective therapy for preventing mTOR inhibitors related pneumovax in cancer patients. However, until now, there is no specifically designed study to investigate the role of pneumovax for these patients, and studies focus on this issue is still needed. Besides antitumor properties, mTOR inhibitors, especially sirolimus, have been widely used as an immunosuppressant in solid organ transplantation to prevent immunemediated graft rejection. Interesting, sirolimus-associated pneumonitis has also been observed in renal and heart transplant recipients, and two deaths in patients who received sirolimus after heart transplants have been reported. However, the overall incidence of treatment mortality associated mTOR inhibitors is very low, and the use of sirolimus in transplant recipients is safe and tolerable. This meta-analysis has some limitations. First, determining whether FAEs are attributable to mTOR inhibitors is particularly difficult in our study. Despite recommendations in the CTCAE version three, the attribution of fatal events to particular toxicities was lacking in the majority of studies. Some studies did not clearly differentiate disease-related from nondisease- related fatal events. The lack of consistent reporting likely, in part, reflects the real-world difficulties of assigning causality to patient deaths, when the precise cause of death is unknown, or the cause of death may be easily associated with either the disease under study or the treatment being explored. However, in the current analysis, identical rules were utilized for abstracting events on both the mTOR inhibitors and control arms which should have impacted over- or under-reporting of events on the mTOR inhibitors and control arms equally. Second, the ability of this study to detect variants in the FAE rate on the basis of specific drug or malignancy was limited because of low statistical power. Given that the conserved mechanism of action and known toxicities among the two study drugs are similar, it is unlikely that significant differences in FAEs would arise between them if more studies were available for analysis. As more high-quality studies of mTOR inhibitors in different malignancies and clinical settings become available, further analyses could be preformed to confirm the trends observed here. Third, the process by which investigators attribute FAE causality is a variable practice since FAEs were not the primary end point of any of the included studies. In addition, a continuity correction of 0.5 subjects with an event is used, which may have slightly overestimated the actual event rate of individual trials. Fourthly, although FAEs are prospectively collected for each individual study, this analysis is retrospective, and there are potentially important differences among the studies, including differing tumor types, dosage and administration schedule of mTOR inhibitors, periods of study conduct and study investigators. All of these would increase the clinical heterogeneity among included trials, which also made the interpretation of a metaanalysis more problematic.