Comment on "The risk of malignancy in patients with IgG4-related disease: a systematic review and meta-analysis" by Yu et al.

With great interest, we have read the recent article "The risk of malignancy in patients with IgG4-related disease: a systematic review and meta-analysis" by Yu et al. While we have a great appreciation for the work conducted by the authors there are some methodological issues need to be considered. First, the period of articles included in the study, almost before 2013, implied that most follow-up days in these articles were earlier than the established date of a unified definition of IgG4-RD, 2011. Thus, it may lead to misclassification bias in the study. Second, IgG4-RD is a fibrous-inflammatory process that often involves multiple organs; however, malignant tumors related to IgG4-RD proposed in the study were only confined to four diseases. Therefore, we suggest adding subgroup analysis for more malignancies depending on the prevalence of IgG4-RD involved organs to ensure better clinical practice. Third, the causation between IgG4-RD and malignancy remains obscure currently. The time course for development in different malignancies varies significantly so that we cannot infer that malignancies discovered after IgG4-RD are directly relevant. With problems mentioned above, we recommend solutions to make this article more convincing.