To the best of our knowledge, this is the first study to use two-sample MR to analyze the causal relationship between autoimmune diseases (sarcoidosis, GD, MS, psoriasis, RA, SjS, SLE, T1D, and CD) and gastrointestinal cancers (CRC, colonic pseudopolyposis, CR-NETs, carcinomas, and GISTs) in European populations using the FinnGen and IEU Open databases.
Currently, the overall prevalence of AIDs is approximately 3–5%, and there is a significant familial tendency [27, 28]. Moreover, AIDs can lead to alterations in the gut microbiota [29], which in turn can have complex effects on the development of gastrointestinal cancer, particularly because of their impact on the intestinal mucosa [30]. Current research on the etiology of CRC is extensive, and inflammatory bowel diseases related to AIDs are recognized as high-risk factors. Our study found that GD also contributes to the incidence of CRC (OR = 1.04, 95% CI = 1.02–1.06, P = 0.001), consistent with Munoz et al.'s report that GD can promote the occurrence of malignancies [31]. One possible reason is that GD promotes the expression of cathepsin B (CB), which is frequently found in CRC. Previous studies have shown that CB can enhance the invasiveness of malignant cells into tissues [32, 33]. However, our study suggests that sarcoidosis and psoriasis may have a protective effect against CRC (IVW OR = 0.97, 95% CI = 0.95–0.99; OR = 0.95, 95% CI = 0.94–0.97, respectively; P = 0.008 and 2.34E-06, respectively). Sarcoidosis is a chronic inflammatory disease of unknown etiology, characterized by widespread and localized inflammatory responses and cytokine secretion. This protective effect may be attributed to the impaired function of myeloid dendritic cells and their imbalance with regulatory T cells, leading to decreased cellular immune function [34]. However, Mathew et al. found that T cell function in patients with sarcoidosis remains relatively unchanged [35], which may help combat the development of CRC. Additionally, Zielonka et al. observed a significant increase in the production of monocytes in the peripheral blood of patients with sarcoidosis (P < 0.05), which was most prominent in stage II disease [36].Our findings suggest that patients with psoriasis have a reduced risk of CRC, which is inconsistent with a meta-analysis of a previous observational study [37]. Several complex factors may have contributed to this inconsistency: 1). P53 expression is increased in patients with psoriasis [38]; 2). Psoriasis is more prevalent in younger individuals, while colon cancer typically affects older populations; and 3).CRC has been associated with alcohol consumption, smoking, and obesity [39]. In the absence of adjustments for these risk factors, several studies have not found a significant association between psoriasis and CRC [40-42].
The precise mechanism of colonic pseudopolyp formation currently remains unknown; however, it is believed to involve non-tumorous lesions formed by the colonic mucosa after repeated inflammation and ulceration during the healing process. Pseudopolyps are also considered at risk for developing CRC [43], and large pseudopolyps can cause severe intestinal obstruction. This study demonstrated that SLE, RA, T1D, and GD were associated with a reduced risk of colonic pseudopolyps (IVW OR = 0.68, 95% CI = 0.51–0.91; OR = 0.83, 95% CI = 0.72–0.95; OR = 0.87, 95% CI = 0.78–0.98; OR = 0.73, 95% CI = 0.64–0.84, respectively; P = 0.010, 0.008, 8.10E-08, and 5.60E-06, respectively). Possible reasons for this finding may be as follows: 1). Macrophages in patients with SLE exhibit a significant proinflammatory role during the onset of the disease and tend to shift toward an anti-inflammatory phenotype during treatment or recovery [44]. 2). Before the onset of these diseases, low levels of inflammatory factors in the blood can promote immune system activation and autoantibody production, creating an "anti-inflammatory" state in parts of the body that are not typically affected. 3). Some studies have shown that patients with T1D have elevated levels of mast cells [45], which play a crucial role in anti-inflammatory responses in the gastrointestinal tract [46]. Additionally, the abundance of bifidobacteria is positively correlated with the incidence of T1D, and an increase in bifidobacteria can further enhance immunity [47, 48]. 4). Immunoglobulins in patients with GD may activate the insulin-like growth factor-1 receptor, and autoantibodies against this receptor contribute to fibroblast activation [49]. This study also indicated that CD, sarcoidosis, psoriasis, and MS pose a risk for the development of colonic pseudopolyps, with the following odds ratios: CD (IVW OR = 1.16, 95% CI = 1.10–1.22; P = 8.10E-08), sarcoidosis (OR = 1.18, 95% CI = 1.03–1.36; P = 0.019), psoriasis (OR = 1.54, 95% CI = 1.32–1.78; P = 2.15E-08), and MS (OR = 1.27, 95% CI = 1.12–1.44; P = 0.001). The possible reasons for this are as follows. 1). CD causes dysbiosis, which further exacerbates intestinal inflammation [50, 51]. 2). In sarcoidosis, T cells are suppressed by transforming them into regulatory T cells [52, 53]. 3). Psoriasis, a representative skin inflammatory disease, involves the circulation of immune cells and inflammatory cytokines from the skin throughout the body, which can promote the development of systemic inflammatory diseases [54-56]. 4). Patients with MS have numerous proinflammatory cells, including Th1 and Th17 cells, that act throughout the body [57, 58].
Although CR-NETs are rare, poorly differentiated neuroendocrine carcinomas have a poor prognosis. CR-NETs are the fastest-growing among all NETs and are the second most common NETs in China [59]. The development of CR-NETs is very slow, and most cases are asymptomatic, often discovered incidentally during colonoscopy screening for CRC. Some individuals may experience anal discomfort, rectal bleeding, or changes in bowel habits. Since up to 90% of NETs are <10 mm, they are typically seen during colonoscopy as small, round, polypoid-like lesions with a smooth appearance and normal or slightly discolored mucosa [60, 61]. This often leads to endoscopic misdiagnosis of intestinal polyps during colonoscopy, causing delays in treatment [62]. When the tumor size is >20 mm, the patient’s prognosis is significantly poor [63]. An increased risk of rectal NETs development is associated with metabolic syndrome. In addition, NETs are associated with hereditary neuroendocrine syndromes [64]. This study demonstrates that sarcoidosis, SjS, and T1D are associated with a reduced risk of developing CR-NETs and carcinomas, with odds ratios as follows: sarcoidosis (IVW OR = 0.93, 95% CI = 0.86–0.99; P = 0.032), SjS (OR = 0.92, 95% CI = 0.86–0.98; P = 0.011), and T1D (OR = 0.92, 95% CI = 0.87–0.97; P = 0.002). Possible reasons for this are as follows. First, sarcoidosis is characterized by the expression of several somatostatin receptors [65]. Somatostatin has inhibitory (growth arrest) and cytotoxic (apoptosis) effects on cells and can suppress the release of growth factors, inhibit angiogenesis, and regulate immune cells [66]. Second, SjS is characterized by high expression of absent in melanoma 2 (AIM2), which enhances certain immune functions, such as antitumor activity and the initiation of immune responses. This may have an inhibitory effect on CR-NETs and carcinomas [67]. Third, T1D often affects young patients and can lead to severe complications in multiple systems, potentially reducing the lifespan. In contrast, CR-NETS and carcinomas typically occur in older adults. Therefore, early mortality associated with T1D may contribute to a reduced incidence of CR-NETs and carcinomas. However, this study indicates that CD and MS may promote the occurrence of CR-NETs and carcinomas (IVW OR = 1.03, 95% CI = 1.01–1.06; OR = 1.07, 95% CI = 1.01–1.14; P = 0.012 and 0.031, respectively). The possible reasons for this are as follows. First, in patients with CD, long-term malabsorption and malnutrition, increased intestinal permeability, chronic intestinal inflammation, endocrine disorders, and dysbiosis may contribute to the development of metabolic syndrome and the occurrence of CR-NETs and carcinomas [68]. Second, MS is often associated with hypertension and hyperlipidemia [69], and the interrelationship between these conditions remains unclear. The presence of vascular disease can increase the risk of CR-NETs and worsen the progression of MS [70].
GISTs are malignant tumors of the digestive tract. These are the most common mesenchymal tumors and sarcomas [71]. GISTs and sarcomas often lead to gastrointestinal bleeding, abdominal pain, weight loss, and intestinal obstruction. This study indicates that sarcoidosis, SjS, and MS are associated with a reduced risk of developing GISTs and sarcomas (IVW OR = 0.82, 95% CI = 0.76–0.89; OR = 0.87, 95% CI = 0.81–0.94; OR = 0.89, 95% CI = 0.83–0.96; P = 4.92E-07, 0.001, and 0.002, respectively). The possible reasons for this are as follows. First, as mentioned previously, patients with sarcoidosis often have intact T-cell function, significantly enhanced generation of peripheral blood mononuclear cells, and abundant expression of somatostatin receptors. These characteristics contribute to tumor growth suppression. Second, in some patients with SjS, elevated interferon levels have been observed, which significantly enhance immune function [72]. Third, natural killer cells play a protective role in patients with MS [73]. Similarly, natural killer cells in patients exhibit antitumor effects. This study also showed that RA is associated with an increased risk of developing GISTs and sarcomas (IVW OR = 1.13, 95% CI = 1.05–1.22; P = 0.002). The possible reasons for this are as follows. First, elevated levels of gastrointestinal tumor markers (CEA, CA199, CA15-3, and CA125) are often found in patients with RA [74], although the exact relationship between these markers and tumor occurrence is unclear. Second, immunosuppressive anti-RA treatments may suppress the ability of the immune system to monitor the body’s internal environment and destroy malignant cells, thereby creating an internal environment conducive to tumor development.
Persistent inflammation associated with RA can promote WNT5A signaling [75], which is involved in the development of multiple malignancies [76]. For example, the correlation between RA and lymphoma has been widely recognized. Interestingly, our research indicates that CRC may promote the occurrence of sarcoidosis (IVW OR = 1.11, 95% CI = 1.01–1.21, P = 0.024). Sarcoidosis is primarily caused by abnormal immune responses that trigger immune reactions in the affected organs, leading to cell aggregation, proliferation, differentiation, and the formation of granulomas. In early CRC, activation of the WNT pathway through intestinal epithelial cells can result in the loss of intestinal barrier function, allowing for the interaction of gut microbes, immune cells, and cytokines. Simultaneously, an increase in inflammatory factors can accelerate tumor growth [77]. Furthermore, tumors can trigger an inflammatory tumor microenvironment (TME) and rely primarily on intercellular interactions within the TME to promote local tumor growth and the formation of distant metastases [78]. In the later stages of tumor development, the loss of P53 function in colon cells can compromise the integrity of the epithelium, facilitating microbial activation of the NF-κB and STAT3 pathways and further triggering inflammation [79]. CRC shapes the internal inflammatory environment, potentially leading to abnormal immune responses and triggering reactions in the affected organs, which may promote the occurrence of sarcoidosis. Additionally, the tumor itself creates an immunosuppressive phenotype, protecting it from .
Co-localization analysis did not reveal any definitive significance, leading us to believe that there was no direct correlation between AIDs and gastrointestinal tumors at the genetic level. Nevertheless, statistically significant associations between these diseases were observed in our study, indicating that their potential relationship requires further research.
Our study offers several key advantages. First, by employing an MR design, we avoided the confounding factors and reverse causality issues that often affect observational studies. Second, our sensitivity analyses considered potential influencing factors, which enhances the robustness of our results. Third, Bayesian co-localization analysis indicated no direct genetic correlation between AIDs and gastrointestinal tumors, although other effects of AIDs on the body might influence gastrointestinal tumor risk, offering valuable insights for future clinical treatment. Finally, using the Finngen database, which includes over 200,000 participants, ensured the reliability of our findings.
However, the study also had some limitations. First, we primarily utilized data from the Finngen R10 database and IEU (2011) open GWAS data. The IVs used in our study were derived from European samples, which may have resulted in data overlap. Second, because our sample originated in Europe, the generalizability of our conclusions to other ethnic groups remains to be validated. Third, the absence of a causal relationship between certain diseases in our study may have been due to insufficient sample sizes. Further research is required to explore these relationships further.