PGI-DLBCL is an aggressive malignancy and commonly shows with some nonspecific clinical manifestations, such as gastric pain, dyspepsia, weight loss, gastric perforation, gastrointestinal bleeding and so on, possibly as a consequence of late diagnosis [32]. Additionally, PGI-DLBCL presents as a clinically heterogeneous tumor, which is generally treated with the standard CHOP or R-CHOP regimen [33]. Despite an improvement in the clinically comprehensive treatment of PGI-DLBCL, the prognosis of refractory or relapsed disease remains poor [34,35]. Hence, further researches are urgently needed to explore the molecular mechanism of PGI-DLBCL development and search for novel prognostic biomarkers and/or potential targets, ultimately making effective individual treatments to improve outcomes.
At present, researchers have found a large number of lncRNAs and proved that they were related to the occurrence and development of human diseases, especially in cancers, which could promote cancer cell proliferation, invasion and metastasis [36]. Emerging reports have shown that lncRNAs can be used as biomarkers to predict the diagnosis and prognosis of human tumors as well as therapeutic targets for tumor treatment. In this study, we discovered that the expression of MALAT1 in PGI-DLBCL was significantly higher than that in adjacent nontumor tissues, and ROC curve analysis showed that the AUC value was 0.882, indicating that MALAT1 has potential diagnostic value for PGI-DLBCL. Moreover, we observed that MALAT1 is tightly related to some clinical parameters, including pathological subtypes, Lugano staging status, IPI score and bone marrow metastasis. Through the Kaplan-Meier analysis, the results indicated that patients with high MALAT1 expression had worse OS and PFS than those with low MALAT1 expression. Combined univariate and multivariate analysis revealed that MALAT1 expression and IPI score were risk factors for OS and PFS in patients with PGI-DLBCL.
As aforementioned, MALAT1 displays a vital role in the pathogenesis and progression of diverse cancers and increasing efforts have been devoted to developing MALAT1-based cancer diagnosis and treatment. However, the mechanism of MALAT1 gene expression affecting prognosis of PGI-DLBCL remains to be fully elucidated. Recent studies have validated that MALAT1 was involved in diverse biological processes, including cell proliferation, cell death, cell cycle, migration and invasion, via modulation of certain signaling pathways, including MAPK/ERK, PI3K/AKT, WNT/β-catenin and NF-kB, promoting tumor growth and metastasis [37-42]. MALAT1 has been reported to promote gastric cancer (GC) cell proliferation partly by recruiting SF2/ASF, a crucial member of serine/arginine-rich protein (SR) family proteins, making a potential biomarker and a therapeutic target for GC diagnosis and treatment [43]. In addition, several previous investigations have demonstrated that MALAT1 induces tumorigenesis and evolution through other molecular mechanisms, including binding to the active chromatin sites and regulating alternative splicing [44,45]. It should be noted that MALAT-1 was upregulated in DLBCL cells, and MALAT-1 silencing can decrease chemotherapy resistance by enhancing autophagy [46]. On the other hand, MALAT1 has been verified to induce DLBCL progression by regulation of miR-195 and PD-L1, then promoted epithelial-mesenchymal transition (EMT) process via Ras/ERK signaling pathway [24].
The IPI is the relatively valuable and widely used prognostic tool for almost all subtypes of non-Hodgkin's lymphoma [47]. The limitation is that the IPI evaluation system includes only a small number of clinical features and does not take into account the molecular biology of tumors. Currently, accumulating studies are performed to explore other risk factors affecting survival in PGI-DLBCL. A previous study has shown that the prognosis of patients with non-GCB is worse than that of patients with GCB [48]. Unfortunately, our study displayed no significant difference between MALAT1 expression and pathological subtypes. Ye et al. [49] discovered that MLL2 protein overexpression in PGI-DLBCL was positively related to higher clinical stage and negatively related to elderly patients (age >60 years) survival. Chen et al. [50] study demonstrated that upregulation of Mad2 might facilitate cell proliferation in PGI-DLBCL, and patients with higher Mad2 expression had inferior disease free survival (DFS). Similarly, our findings suggested that MALAT1 was increased in PGI-DLBCL and patients with elevated MALAT1 expression exhibited unfavorable outcomes, indicating MALAT1.
The present study also has some shortcomings: First, due to the limited sample, we can not get enough samples from other extranodal lymphoma patients, leading to fail to evaluate the role of MALAT1 expression in other extranodal lymphomas. Second, this study confirmed that MALAT1 had the predictive potential to PGI-DLBCL prognosis. However, owing to the limitation of samples, the present study does not independently verify the sample settings, and it is impossible to verify whether there are the same results in different samples. This needs to be further verified by expanding the sample size and including other patients with extranodal lymphoma in future studies.
In conclusion, our work presented that MALAT1 can be considered as a novel diagnostic and prognostic biomarker in PGI-DLBCL. A larger sample size is needed in the future in order to better understand the mechanisms of MALAT1 in the molecular etiology of PGI-DLBCL.