In our cohort the dominant histological subtype was astrocytoma (56.6%). Oligoastrocytoma and oligodendroglioma accounted for 28.3% and 15.1%, respectively. It should be taken into account that in the WHO 2021 classification, oligoastrocytoma do not constitute a separate subtype according to molecular criteria and would be classified as oligodendrogliomas or astrocytomas(22). Our findings align with existing epidemiological data, showing a 2–3:1 ratio of astrocytoma to oligodendroglioma occurrence, as reflected in our analysis (23, 24)
A well-known molecular prognostic factors for brain gliomas are IDH 1/2 mutations and 1p19q codeletion. Literature indicates that IDH1 mutations occur in 60–80% of WHO G2/G3 gliomas, while IDH2 mutations are much rarer, with a 1–6% incidence and both decrease with grade(25, 26, 27, 28). This corresponds to the results obtained in our analysis. The presence of 1p19q codeletion was found in 52.2% of gliomas with an oligodendroglial component. It was higher in WHO G2 compared to the WHO G3 gliomas − 75% and 27.3%, respectively, which as well stays in line with literature data (29, 30).
miR-200 family in glioma tissue and accompanying tissue.
Available literature, in many cases, analyzes only one strand of each miR-200 molecule. It should be emphasized that current knowledge about miRNAs is constantly expanding and indicates that both the 5' and 3' strands may be functional and perform compatible as well as distinct regulatory functions (31, 32). Analysis of only single strands of a given miRNA leaves many questions and constitutes an incomplete set of information in relation to many cancer diseases, including gliomas. Conducted own research, in accordance with the latest trends in miRNA characterization, analyzes the expression level of both miRNA strands, which contain a complete set of information.
First, a comparative analysis of each component and its impact on patient prognosis was performed in connection with well-known prognostic factors in the form of clinical and molecular features.
Expression of miR-200 family depending on Grade.
In our own analysis, a significantly lower level of miR-200c-3p expression was observed in WHO G3 gliomas. Wang et al. showed a reduced miR-200a expression in WHO G3 and WHO G4 gliomas. Patients with WHO G2 tumors were not included (33). Similarly, Liu et al., showed a significant reduction in miR-200a-3p expression in glioma tissues with higher Grade (34). Chen et al. showed a decrease in the expression of miR-200a with higher Grade, but most of the patients were with WHO G4 gliomas (35). Regarding miR-200b expression, a study which included patients with G1-G4 gliomas showed its significant decrease with increasing Grade (p = 0.002) (36). Similar results were obtained by Men et al. however, the differences between patients with WHO G2 and WHO G3 gliomas were less noticeable (37). The meta-analysis confirmed the results. There was a decrease in its expression between WHO G1/G2 and WHO G3/4 groups − 5.87 ± 1.77 vs. 3.13 ± 0.89, p < 0.01, respectively (38). Qin et al., compared WHO G2 and WHO G3/4 gliomas and showed a decrease in miR-200c expression with increasing Grade in tissues, as well as in glioma cell lines (p = 0.0064)(39). These results are consistent with our own analysis. In regard to miR-141 expression, negative correlation with higher Grade was found in three studies, two of them included additionally WHO G1 and G4 gliomas (40, 41, 42). One study showed positive correlation between the expression of miR-141-3p and Grade in WHO G1/G2 and WHO G3/G4 gliomas (p < 0.001) (43). Only one report about miR-429 expression was found. Thirty-seven patients with WHO G2 and 24 patients with WHO G3 gliomas were included. Positive correlation of its expression with increasing Grade was found (p < 0.05) (44).
Taking into account presented results, the differences shown may result from the small number of patients included. Additionally, it should be borne in mind that the discrepancies could also be caused by different cut-off points in relation to the assessment of the expression, considered as low or high level. Undoubtedly, the expression of individual components of the miR-200 family, changing with Grade, may be related to carcinogenesis and progression of gliomas, which requires further, broader analysis in the future.
Expression of miR-200 family depending on IDH 1/2 mutation and 1p19q codeletion.
There was no relationship between the expression of miR-200 family and the IDH1/2 mutation. However, a significant increase in the expression of the miR-200a-5p was noted in gliomas without 1p19q codeletion. So far, no combined analysis of miR-200 and IDH 1/2 mutations and/or 1p19q codeletion have been performed, as was done in our study. Undoubtedly the weak point of miR-200 expression studies in gliomas is the lack of reference of the miR-200 expression level to the new molecular classification which was also emphasized in meta-analysis (37).
Prognostic value of miR-200 family based on OS.
In our study, 2- and 5-year OS for WHO G2/G3 gliomas was 94% and 74%, respectively. These data are consistent with the systematic reviews and big cohort studies(45, 46, 47).
With regard to miR-200 family, our analysis showed a significant relationship between the expression of its components and OS. We have shown that WHO G2/G3 gliomas with higher miR-200a-3p and lower miR-200a-5p expression had better prognosis. Unfortunately, there are no publications directly comparing the OS with miR-200a expression. It has been found that the miR-200-3p inhibits the ability of glioma cells to survive, invade and proliferate (35). Similarly, it was shown that its reduced expression in glioma cells was associated with a worse response to chemotherapy and glioma neogenesis and progression (33). Therefore, it seems logical to assume that a reduced level of the miR-200a is associated with the development of clones resistant to systemic treatment, which results in worse OS. Unfortunately, it was not specified which strand the obtained results concerned.
Our analysis showed no relationship between the expression of both miR-200b and OS. Similar results were presented by Wang et al., in patients with WHO G1/G2 gliomas but higher expression of miR-200b led to better OS in WHO G3/G4 gliomas (p = 0.028) (36). It should be also noted that this is the only study that reported a significantly higher expression of miR-200b in glioma tissues compared to non-cancerous tissue, unlike the rest of the available literature data regarding this component (36). Men et al. showed that low miR-200b expression led to shorter 5-year OS and 5-year PFS in WHO G3/G4 gliomas. There were no differences in WHO G1/G2 group. These differences for PFS and OS in patients with it’s low expression compared to high expression group were 9.61 months (95% CI, 6.9–12.8) and 13.89 months (95% CI,11.06–17.83) and 14.66 months (95% CI, 9.82–20.92) and 20.19 months (95% CI, 13.68–26.29) (p = 0.023 and 0.012), respectively (37). However, it should be considered that histological types among WHO G2/G3 gliomas included only astrocytomas and anaplastic astrocytomas, without information regarding IDH mutation and 1p19q codeletion (37).
Our findings showed that low miR-200c-5p expression correlated with better prognosis. This is the first report of this type. Its important role in gliomagenesis and prognostication was previously highlighted (39). However, also patients with WHO G4 gliomas, ependymocytomas and anaplastic ependymocytomas were included (39).
We have also noted that higher miR-141-3p expression correlates with better OS. There is no other literature involving its impact on OS. However, there is research that may indirectly explain obtained results. It was previously shown that high miR-141 expression can strongly inhibit the proliferative and invasive potential of gliomas diminishing their ability to progress (40, 48).
High levels of miR-141-3p inhibits glioma tumorigenesis, which has been linked with miR-141-3p/YAP 1 regulation (42). It has been also shown, in vitro and in vivo, that miR-141-3p can inhibit formation of new vessels, cell division cycle and induce apoptosis of glioma cells. Mutual inverse correlation between miR141-3p and the EphA2 gene was detected (48).
Our study reported better 2- and 5-year OS in patients with lower miR-429 expression. Sun et al. showed a significantly higher probability of 5-year OS was noted in patients with low miR-429 expression (p < 0.001). The multivariate analysis confirmed correlation of miR-429 expression with OS (RR: 3.674, 95% CI: 1.990–6.784, p = 0.001) (44). A relationship between miR-429 and BMK-1 kinase expression was previously described by other authors. Material derived from cell lines and paraffin blocks of WHO G1-G4 gliomas were used. Also in this study a higher miR-429 expression led to better OS (p = 0.000) (49). Described results indicate an important role of miR-429 as a prognostic factor for OS of WHO G2/G3 gliomas.
Expression of one type of miRNA and its interactions with another may lead to contrasting prognostic value in different cancers and when compared to the determination of just single miRNAs. Therefore, studies that integrate a larger number of miRNA and clinicopathological features provide the highest prognostic and predictive value. This allows for the creation of reliable models that more accurately determine the prognosis of patients with a given group of variables, as indicated by meta-analyses (50, 51, 52). In our study, for the first time, the entire panel of the miR-200 family, including both strands, was used to create a logistic regression model estimating the probability of OS. The model based on all components had a sensitivity of 63% and a specificity of 78%. Moreover, the predictive potential of the signature reached AUC = 0.703. This indicates that the selected miRNA signature has a relatively high potential to distinguish patients according to prognosis. Patients with a lower model value had a significantly better prognosis. The difference in 2- and 5-year OS in the group with a low compared to high model value was 24% and 17%, respectively.
This indicates the potential clinical usefulness of the presented model when considering treatment strategies. Taking into account the multitude of gliomas clinical features and the range of therapeutic effects there is a strong need to search for prognostic models helping to decide whether adjuvant radiotherapy/ chemotherapy should be used and what types, doses and duration should be chosen. Perhaps the intensification of treatment in patients with a higher model value would lead to better results. However, this hypothesis requires testing in prospective clinical trials.
In the final step, clinicopathological features were integrated with miR-200 expression allowing more precise OS prediction. The 9 stages, backward stepwise elimination model, confirmed the strong predictive value of TV and CTV.
The impact of TV on OS of glioma patients have been previously described in the literature. Flores et al. showed that worse OS occurred in patients with TV ≥ 60 cm³ and/or ≥ 2000 mm² in the T2-Flair sequence before surgery (HR 3.72 and 3.93) (53). Another study demonstrated the worst OS when tumors were larger than 5 cm (HR = 1.56, 95% CI 1.12–2.19, p = 0.0089) (54). However, it should be borne in mind that there are also reports showing that there is no relationship between TV, extent of resection and OS in patients with anaplastic astrocytomas (55).
Chapman et al. showed a relationship between PTV and OS in HGG. For non-stereotactic techniques, PTV above 131cc significantly correlated with worse OS (56). Guram et al. showed no significant difference in OS depending on PTV created by addition of 0.4 cm, 1 cm or 2–3 cm margin in HGG (57). In our work, CTV was chosen, which corresponds better with the OS than the PTV. The relationship of CTV with OS and PFS, was analyzed in the work by Liu et al. Two groups, CTV defined according to the EORTC guidelines as a bed with edema and a 2 cm margin, and the other similar but in which edema was not included, were selected. During the median follow-up of 26.4 months, no differences in OS and PFS were shown (p = 0.418, p = 0.388) (58).
The presented reports, which are ambiguous, encourage clinical trials involving evaluation of CTV and the results of therapy. Perhaps smaller volumes may be used in patients treated for certain types of gliomas, depending on the planned adjuvant therapy regimen.
In our final ANOVA model, apart from TV and CTV, miR-200a-5p, miR-200b-3p, miR-141-3p and miR-429 were predictors of OS (p = 0.054). This model is the first tool of its kind that can be helpful in prediction of OS. Its use may help clinicians in difficult decisions related to the treatement intensification or de-intensification.
A limitation of our study is the relatively small sample size and the lack of analysis based on different therapeutic regimens. However, it remains the most comprehensive analysis of the miR-200 family available. It should be borne in mind that in WHO 2021 classification, some of included patients would be switched to other glioma types. Future trials should be conducted prospectively, on a larger cohort, taking into account all of the molecular features implemented in WHO 2021 classification and detailed data on adjuvant treatment.