In the present study, we first observed a significantly increased prevalence of malignancies based on the largest multicenter cohort of Chinese IgG4-RD patients. We reported higher eosinophil percentage and more frequent AIP presented in IgG4-RD patients with malignancies. However, elevated serum AGR was a potential negative correlation factor for malignancy in IgG4-RD patients.
In this study, we observed a significantly increased prevalence of total malignancies in our cohort compared to the general Chinese population (SPR 8.66 [95% CI 5.84, 12.31]). We summarized the types of malignancies in our cohort and compared it between IgG4-RD patients and the general Chinese population. Similar to epidemiological studies of general population, lung cancer was the most common malignancy in IgG4-RD patients. However, lymphoma accounted for 10.3% (three cases) of the malignancies in our cohort, given a standard prevalence ratio of 42.86 (95% CI 8.79, 123.88). Several previous studies suggested discrepancies in the types of malignancies between patients with IgG4-RD and the general population [1, 11,12,13]. Besides, the distribution of malignant tumors in IgG4-RD observed in previous studies is varied. Wallace et al. [10] reported that prostate cancer and lymphoma were the most common malignancies based on a United States cohort, whereas only one prostate cancer case was observed in our study. Additionally, our cohort reported that lymphoma, thyroid, and stomach cancer were frequent malignancies associated with IgG4-RD, consistent with study by Ahn et al. [1]. The disparities may be explained by differences of race, environment, and sample capacity.
To date, the pathogenesis on the association between IgG4-RD and malignancy remains obscure. The chronic inflammatory state of IgG4-RD may play an important role in the development of malignancies. According to previous studies [19,20,21,22,23], mediators produced by activated inflammatory cells promote a variety of damages, including genetic mutations, post-translational modification of proteins involved in apoptosis, DNA repair, cell cycle control and signal transduction, as well as DNA and histone methylation, generating a pathologically conducive microenvironment, which may induce the growth and progression of malignancies. Several previous studies suggested that chronic antigenic stimulation, together with oncogenic events such as p53 inactivation and K-ras mutation in IgG4-RD, led to an increased risk of malignant transformation compared with the general population [9, 24]. Almost half of our patients developed malignancies after IgG4-RD diagnosis. Inflammation-associated oncogenesis may provide explanations for these cases.
In our study, three IgG4-RD patients developed lymphoma, including two B cell-derived non-Hodgkin’s lymphoma (NHL) cases and one Hodgkin’s lymphoma (HL) case. To our knowledge, few studies revealed close relationship between IgG4-RD and development of B cell lymphoma [25, 26]. Interestingly, as indicated by previous studies, an increased risk of lymphoma is also observed in patients with other autoimmune and inflammatory diseases [27, 28]. Goldin et al. emphasized the effects of secondary inflammation due to autoimmune stimulation on the processes, such as cytokine and chemokine release and viral reactivation (Epstein–Barr virus, for example). In addition, germline and somatic mutations are likely to induce autoimmunity and lymphomagenesis. Now that activation of B cells by increased Th2 cytokines including interleukin-4, 5, 10, and 13 contributes to the pathogenesis of IgG4-RD [29, 30], the superiority of B cell lymphoma as a secondary condition to IgG4-RD seems explicable. A study by Conde et al. identified the common genetic variants between NHL subtypes and autoimmune diseases, demonstrating a potential shared genetic mechanism [31]. A study reported the reciprocal chromosomal translocation t (14;19) (q32;q13.1) for rearrangements of IgH and BCL3 genes in the DLBCL cells, generating the dysfunction of the protein involved in nuclear factor (NF)-κB family regulation and complex cytogenetic abnormalities [26]. Accumulation of similar events may promote the process of lymphoma development from IgG4-RD. Moreover, the functional disorders of immune system in IgG4-RD may influence the interactions between components in the microenvironment and promote lymphomagenesis [32, 33]. The association between IgG4-RD and specific lymphoid malignancies and the potential etiologic mechanisms deserve further discussion.
Several studies have found that AIP is associated with an increased risk of malignancies [3, 34]. In AIP patients, high levels of K-ras mutation have been detected in gastrointestinal tract, associated with persistent IgG4-related fibroinflammation and abundant infiltration of T lymphocytes and Foxp3+ cells, indicating that AIP may share a similar molecular pathogenesis with malignancies in IgG4-RD.
It is proved that eosinophils play a pivotal role in several immunological diseases and malignancies [35]. Several previous studies observed eosinophilia in patients with both solid tumors and lymphoma [36,37,38]. On the one hand, eosinophils exert great influence in tumoricidal response. On the other hand, eosinophils contribute to tumor angiogenesis through the release of proangiogenic molecules such as vascular endothelial growth factor (VEGF) and osteopontin (OPN), and promote endothelial cell proliferation [39, 40]. Accordingly, in this study, we found obviously elevated eosinophil percentage in IgG4-RD patients with malignancy. It is worth noting that eosinophilia may contribute to different clinical patterns in IgG4-RD patients as Zhang et al. reported [41]. As a possible marker of disease severity, the role of eosinophil in the development of malignancy relies on further pathological and molecular confirmation.
In this study, we observed higher serum globulin levels in IgG4-RD patients with malignancies. Besides, serum AGR was lower in patients with malignancies than those without, which is consistent with previous studies [42, 43]. As a pro-inflammatory factor, globulin consists of a variety of components, including acute-phase reactive proteins, immunoglobulins, interleukins, and tumor indicators, and participates in the regulation of osmotic pressure and the transportation of various compounds [42]. It is widely known that an increased level of globulin is related to chronic inflammation and various types of malignancies, especially hematological tumors. As serum globulin secreted by tumor-related cells is reported to promote the development, angiogenesis, immunosuppression, and metastasis of malignancies, high serum globulin may indicate the extent of severe chronic inflammation and poor prognosis [43]. As an important component, immunoglobulin G (IgG) expressed by cancer cells is reported to promote growth and survival of malignancies, by interacting with proteins involved in cell growth (RACK1, RAN and PRDX1, etc.) and activating the relevant signaling pathway. Down-regulation of IgG may arrest the S-phase of the cell cycle. In addition, several studies have reported IgG4 as a significant prognostic indicator in neoplastic disorders [44, 45]. Wu J et al. demonstrated that elevated serum IgG4:IgG ratio may predict poor clinical outcomes and recurrence of hepatocellular carcinoma (HCC) [46]. However, IgG and IgG subclass concentrations may differ according to sex and race. As reported, Asians with IgG4-RD have higher IgG and IgG4 production in general than white people, which may limit transferability of this finding to North American/European contexts [7, 47, 48].
This study has several limitations. First, as a retrospective study, it could not overcome the typical flaws inherent to the design itself. Second, examinations of the whole body, even the FDG-PET, may lead to the detection bias. Third, as an inevitable issue for a rare condition, low number of malignancies and wide 95% CI ranges were reported in our study. Moreover, the model was validated only internally. Collection of data based on an independent cohort for further verification is under way. In consideration of the low incidence of both IgG4-RD and malignancy, the nomogram for assessing malignancy risk in IgG4-RD deserves long-term verification and adjustment.