1. IntroductionGlioma is the most common primary malignant tumor of the adult central nervous system (CNS). Due to its invasive growth, most patients will recur even after combined treatments such as surgery, radiotherapy, chemotherapy, targeted therapy, and immunotherapy [1]. The latest edition of the WHO classification of tumors of the CNS in 2021 divided gliomas into grades 1–4, from low to high grade [2]. Most adult gliomas are high-grade, fast-growing, and aggressive. The current standard treatment for adult HGG is surgery within the maximum safety range, followed by radiotherapy and concurrent temozolomide (TMZ) chemotherapy, and six cycles of TMZ adjuvant chemotherapy (Stupp protocol) [3]. Despite standardized treatment, the median survival of HGG patients was only 14.6 months [4].Surgery is the basis of the standard treatment for glioma, which is closely related to the prognoses of patients [5,6]. Multiple retrospective studies and large-scale meta-analyses have shown that extended surgical resection can significantly prolong the progression-free survival (PFS) and overall survival (OS) of glioma patients compared with partial resection or biopsy [7,8,9,10,11]. In addition, radiotherapy plays an important role in the treatment of glioma and can kill or inhibit residual tumor cells and prolong the survival of patients [12,13,14]. In addition, TMZ is currently the first-line single-agent chemotherapy drug for glioma, with the advantages of low toxicity and strong anti-tumor activity [15,16]. However, there has been controversy over the optimal number of cycles of postoperative TMZ adjuvant chemotherapy.IDH is an important indicator of glioma molecular classification, which plays a significant role in the diagnosis, individualized treatment, and prognosis of gliomas [17]. Studies have shown that IDH-wildtype gliomas are more prone to recur than IDH-mutated gliomas [18]. MGMT is a DNA repair enzyme and is mainly distributed in the cytoplasm, repairing DNA to maintain the stability of the genome in cells. If the MGMT promoter is methylated, it will cause the loss of MGMT expression, resulting in a decrease in DNA repair and making gliomas more sensitive to chemotherapy drugs such as TMZ [19,20]. It is generally believed that patients with methylation of the MGMT promoter respond better to TMZ treatment [21].

We included both the grade three and four gliomas in the analysis, as they are all managed with the same treatment in China (the Stupp protocol). In order to identify the critical factors associated with the prognosis of HGG patients who have received standard treatment, we retrospectively analyzed the relevant data of patients, including basic information, tumor resection extent, tumor grade and genotyping, the interval between surgery and radiotherapy, postoperative TMZ adjuvant chemotherapy cycles, and radiological data. Furthermore, a novel web-based individualized survival prediction calculator was also developed and validated for these patients.

4. DiscussionGlioma is the most common primary CNS tumor originating from glial cells, accounting for 80% of primary intracranial tumors [23]. The clinical characteristics of HGG are highly malignant and prone to recurrence, which makes the treatment very tough. In recent years, molecular detection of glioma has achieved a certain degree of development, including MGMT promoter methylation, co-deletion of 1p/19q, IDH mutation, TERT promoter mutation, EGFR amplification, etc. This molecular information plays an important role in the prognosis and treatment of glioma [24,25,26]. In the WHO classification of tumors of the CNS in 2021, the integration of histopathology and molecular classification makes the diagnoses more objective, which is of great significance for guiding individualized treatments and evaluating prognoses.The standard treatment for glioma includes surgery, radiotherapy, and TMZ-based chemotherapy. Surgery is the basis of the standard treatment of glioma, which is closely related to the prognoses of patients. The research by Sanai et al. [7] indicated that for patients with newly diagnosed GBMs, aggressive EOR equated with an improvement in overall survival. Hardesty et al. [8] reviewed every major peer-reviewed clinical publication from 1990 to 2012 on the role of EOR in glioma outcome and concluded that more extensive surgical resections weres associated with longer life expectancies for both low- and high-grade newly diagnosed gliomas. A meta-analysis of the association between the EOR and outcome of patients with glioblastoma (GBM), which comprised 41117 unique patients, showed that gross total resection substantially improved OS and PFS, compared with subtotal resection [10]. In our study, EOR was strongly associated with PFS and OS in HGG patients receiving standard treatment, consistent with the literature. Glioma shows invasive growth, and the tumor boundary is generally difficult to judge by conventional radiology. Therefore, the resection scope of a tumor is often limited to the tumor boundary indicated by a preoperative radiological examination, rather than the accurate histopathological boundary, which may be one of the important reasons for the easy recurrence of glioma after resection [27]. Therefore, a more extensive and more thorough resection of a tumor within the safety range can fundamentally reduce the probability of tumor recurrence, improve patient prognosis, and prolong patient survival.A clinical trial by Stupp et al. [28] showed that patients with GBM who received concurrent TMZ and radiotherapy followed by 6 cycles of TMZ adjuvant chemotherapy had a median survival of 14.6 months and a 5-year survival rate of 9.8%. This study was a milestone in the development of glioma therapy. Many researchers also suggested that the cycle of TMZ adjuvant chemotherapy should be extended to 12 cycles [29]. A recent meta-analysis of the number of adjuvant TMZ cycles in newly diagnosed GBM, which consisted of 882 patients (461 patients for the standard chemotherapy group and 421 patients for the extended chemotherapy group), demonstrated that the extended TMZ regimen was associated with a non-significant improvement in PFS without a corresponding improvement in OS [30]. A prospective, randomized, multicenter phase II clinical trial (GEINO 14-01) compared the effect of using the standard regimen with long-cycle TMZ adjuvant chemotherapy on GBM patients and concluded that there was no statistical difference between the two treatment regimens in terms of six-month progression-free survival (PFS-6), PFS, and OS [31]. However, the study by Roldán et al. [32] showed that the median OSs of the TMZ long-cycle regimen group and the standard regimen group were 24.6 months and 16.5 months, respectively, and the difference was statistically significant (pp > 0.05). Hence, the necessity of long-cycle TMZ adjuvant chemotherapy requires verification by more large-scale, multi-centered, and prospective studies.IDH is a key rate-limiting enzyme in the tricarboxylic acid cycle, which catalyzes the oxidative decarboxylation of isocitrate to generate α-ketoglutarate and CO2, providing energy for cellular metabolism and precursors for biosynthesis [17]. IDH mutations are common in astrocytoma, oligodendroglioma, and secondary GBM [33]. The review by Śledzińska et al. [34] indicated that for adult patients, IDH mutations were positive prognostic markers and had the greatest prognostic significance. Chen et al. [35] found that the median survival time of glioma patients with IDH mutations was significantly higher than that of those without mutations, which was positively correlated with the survival rate, and the positive rate of IDH mutation decreased significantly from LGG to HGG. Some studies also demonstrated that patients with IDH-mutant primary GBM who received postoperative radiotherapy and chemotherapy had a longer PFS and OS [36,37]. In our study, patients with IDH mutation had a longer PFS and OS than those without IDH mutation, and the difference was statistically significant. We supposed that IDH-mutant HGGs may have higher tumor resection rates and may be more sensitive to postoperative radiotherapy and chemotherapy, which effectively prolonged the survival times of patients. MGMT is a DNA repair enzyme and is mainly distributed in the cytoplasm and repairs DNA to maintain the stability of the genome in cells [38]. In normal tissues, the CpG site in the MGMT promoter region is generally in an un-methylated state, but with the occurrence of a tumor, the promoter region is methylated. If the MGMT promoter is methylated, it will cause a loss in MGMT expression, resulting in a decrease in DNA repair and making gliomas more sensitive to chemotherapy drugs such as TMZ [39], and, therefore, the MGMT promoter methylation status was considered as an independent predictor of prognosis in patients with gliomas [40]. A meta-analysis comprising fourteen studies with 1231 GBM patients showed a significant association of MGMT methylation with a better OS with a pooled hazard ratio of 1.66 [41]. Schaff et al. [42] retrospectively identified 54 adult patients with newly diagnosed resected GBM and found that MGMT promoter methylation was statistically significantly associated with PFS and OS. The review by Binabaj et al. [43] indicated that GBM patients with MGMT methylation were associated with longer OS, although this effect was not detected for PFS. In our center, we generally recommend Stupp protocol for HGG patients regardless of whether they have MGMT promoter methylation. However, in this study, we did not find that HGG patients with MGMT promoter methylation had statistically improved PFS and OS compared with those without methylation (p > 0.05). We opined that this issue needed to be validated with a larger, multi-center patient sample size, which we will continue to explore in future studies. TERT promoter mutation is one of the common genetic mutations in adult diffuse gliomas and usually occurs in the promoter region of -124 and -146 base pairs (C228T and C250T), which can enhance TERT transcription [44]. It is essential to note that the prognostic impact of TERT promoter mutation is bivalent according to the IDH status and histological grade. In the latest WHO classification of tumors of the CNS, GBM contains only IDH-wildtype tumors, and IDH-mutant GBM was no longer defined as GBM but defined as astrocytoma, IDH mutation of the CNS (WHO 4). In general, TERT promoter mutations confer survival benefits in patients with IDH-mutant gliomas, while they are negative prognosticators in those with IDH-wildtype tumors [45]. In grade three gliomas with IDH mutations, several studies have reported that TERT promoter mutations are associated with favorable outcomes [46]. Several independent studies have reported the negative impact of TERT promoter mutations on survival in IDH-wildtype GBM cases [47,48,49]. TERT promoter status is generally stable between primary and recurrent tumor tissues in adult-type diffuse gliomas and plays an important role in the very early stages of tumor development in GBMs. In this study, no significant correlation was found between TERT promoter mutation and the survival of patients (PFS and OS). However, we found that patients with IDH and TERT promoter co-mutations had better prognoses (p50,51,52,53]. Hence, for the prognosis stratification of HGG patients, any single indicator may not be able to make a good judgment, and the combination of multiple indicators is more conducive to prognosis stratification [54].The EI represented the degree of the peritumoral brain edema (PTBE) compared with tumor volume, with an index of 1.0, indicating no PTBE development, and was used only in clinical studies related to previous meningioma [55], which has not been applied to the prognosis evaluation of glioma. However, PTBE was a common feature of glioma, especially HGG [56]. Postoperative pathologically confirmed gliomas often entered PTBE beyond the tumor margin visible on radiology, so this area was often the site of tumor recurrence [57,58]. The PTBE of gliomas showed hyper-intensity on the T2WI and FLAIR sequences but no enhancement on the CE-T1WI sequence, suggesting vascular edema and tumor infiltration near the tumor. Previous studies have suggested that the degree of PTBE was related to the PFS of patients, and the more severe the PTBE was, the worse the prognosis was [59,60]. In this study, we found that EI was associated with the PFS of HGG patients receiving standard treatment, and this was the first report on the relationship between EI and PFS in HGG patients. In addition, it was indicated that age was related to the OS of HGG patients receiving standard treatment. A poor physical condition and immunity, a high degree of malignancy of the tumor, and a decline in multiple organs’ functions may be important reasons for the poor prognoses of elderly patients. Based on the research results, we have established free online prediction websites for PFS (https://glioma.shinyapps.io/survival_prediction_tool/, access data: 10 November 2022) and OS (https://glioma.shinyapps.io/survival_prediction_tool_os/, access data: 10 November 2022), respectively, and neurosurgeons can log in anytime and anywhere through computers or mobile phones. After entering patients’ relevant data, they can obtain prediction information associated with HGG patients’ survival. Grasping this information will assist neurosurgeons in optimizing clinical management and treatment strategies and improving the prognoses of patients to a certain extent. The predictive nomograms established in previous studies [4,61,62,63] could not automatically calculate survival time and could not realize the visualization of predicting results, but the current nomogram models can easily implement these functions.

However, our study still has some inevitable limitations. First, this was a retrospective study and not a randomized trial, lending to its inherent limitations. Secondly, the molecular detection information was not complete and did not include 1p/19q co-deletion, ATRX mutation, EGFR amplification, etc., but this molecular information was of great significance to the diagnosis and treatment of glioma, so it needs to be improved in future research. Our cohort included 35 patients with IDH1-mutated grade three gliomas which have a better prognosis and may cause a potential bias. We included this group of gliomas because in China they receive the same treatment as non-mutated IDH1 gliomas. Moreover, the strict exclusion criteria for this study resulted in a relatively small number of eligible patients being enrolled, and multi-centered, prospective, and randomized controlled clinical research on the critical factors relevant to the prognoses of adult HGGs is required to be carried out.