Glioblastoma is the most aggressive primary malignant brain tumor in adults [1]. The current standard treatment for glioblastoma after surgical resection is combined radiotherapy and chemotherapy using temozolamide (TMZ) or TMZ combined with other chemotherapeutic agents. Despite these treatments, glioblastoma remains a fatal disease and the overall survival is approximately 14.6 months within five years [2, 3]. However, the current treatment strategies are considered palliative, with the aim being to improve patient survival and maintain a good quality of life. Several biomarkers are still used in clinical practice to improve the diagnostic and prognostic status of glioblastoma. One of these markers are IDH1^R132H mutation and MGMT gene promoter methylation. The IDH1 gene, which encodes cytosolic NADP + -dependent isocitrate dehydrogenase, was shown to correlate with outcome of patients with glioblastoma [4–6]. The MGMT, which is a DNA repair protein that removes alkyl groups from several residues particularly the O6-position of guanine, is considered the most relevant for the action of an extensively used TMZ [7, 8]. Because IDH1^R132H mutation, is the most common variant mutation detected in most of cancers, particularly glioblastoma, we used specific monoclonal antibody (IMAB-1) targeted R131H residue.

The relationship of MGMT promoter methylation with IDH1 mutation, treatment modalities and survival rates showed controversial results. Some studies revealed that glioblastomas with methylated MGMT promoter were more sensitive to chemotherapeutic agent (TMZ) resulting in a better survival rate [9–11], while other studies revealed that MGMT promoter methylation was not associated with better overall survival (OS) [12, 13]. Combs et al. also found a none-favourable OS in a group of 160 patients with glioblastoma treated with radiotherapy and TMZ. In contrast, Millward et al. demonstrated that the combination of methylated MGMT promoter and IDH1 mutation was associated with considerably longer OS in a series of chemoradiotherapy-treated glioblastoma tumors [14]. Despite this controversy, both biomarkers are still considered prognostic factors in patients with glioblastoma.

In this study, we evaluated the impact of MGMT promoter methylation and IDH1 mutation on the recurrence-free interval in patients with glioblastoma treated with different treatment modalities (radiotherapy and different types of chemotherapies). The chemotherapy protocol included temozolomide (TMZ) alone, or TMZ and other adjuvant therapies included (bevacizumab, irinotecan, lomustine, and etoposide). This study provided an additional justification to the previous controversial results in the literature. To our knowledge, this study is considered as a first research of such type performed in Saudi Arabian patients.

A total of 82 glioblastoma patients with complete resection and who received treatment were included in this study. The patient and tumor characteristics of the study group are listed in Table 1. The mean patient age was 48 years old (<50 years old, n = 32; ≥50 years old, n = 50), and 58.5% of the study group was male (n = 48). IDH1 mutation was found in 32 cases (39%) and the remaining 50 cases (61%) were IDH1 wildtype. The MGMT promoter was methylated in 28 patients (34.1%) and unmethylated in 54 cases (65.9%). After complete tumor resection, 62 patients (75.6%) received chemoradiotherapy while 20 patients (24.4%) only received radiotherapy. Among those who received chemoradiotherapy, approximately 72.5% (n = 45) received TMZ alone while 27.5% (n = 17) received TMZ along with other chemotherapies included bevacizumab, irinotecan, lomustine, or etoposide. Approximately 61% (n = 50) had tumor recurrence after 1 year, while 39% (n = 32) showed recurrence before 1 year of the adjuvant therapies.

Glioblastoma is the most aggressive primary malignant brain tumor in adults [1]. Both primary and secondary glioblastomas are pathologically indistinguishable, but they vary at the molecular level [2]. The disease remains fatal although the palliative treatment modalities given to the patients [2, 3]. These treatments are currently dependent on several molecular markers including IDH1 mutation and MGMT-gene promoter methylation. Despite the controversy on the impact of these biomarkers, they are still considered prognostic factors in patients with glioblastoma. While wildtype IDH1 is present in 90% of primary glioblastomas [1], mutant IDH1 is common in secondary glioblastomas and associated with increased patient survival [4, 6]. Epigenetic-mediated silencing of the MGMT gene in glioblastoma by promoter methylation has also been shown to correlate with better OS. Use of IDH1 combined with MGMT promoter as a stratification factor seems appropriate in clinical trials for the treatment of patients with secondary glioblastoma [6].

In the present analysis, we evaluated the impact of MGMT promoter methylation as well as IDH1 mutation status on recurrence-free interval (the period from beginning of adjuvant therapy after surgical resection to the possible first date of recurrence) in patients with glioblastoma. We used recurrence-free interval (RI) rather than OS as RI is more accurate and also doesn’t provide false predictability in the outcome of glioblastoma patients.

Because our results found that there was no significant relationship between IDH1 mutation and MGMT promoter methylation, both factors are considered prognostically independent (Table 2). This relationship can be considered significant if the age factor was included in the prognostic analysis. For example, we found that more glioblastoma patients younger than 50 years old with IDH1 mutant tumors had tumor recurrence after one year of treatment compared with those with IDH1 wildtype (Figure 2A; Table 3).

The impact of MGMT promoter methylation status in patients with glioblastoma also showed controversial results. Hegi et al. showed that glioblastomas with methylated MGMT promoters were more sensitive to chemotherapeutic agents, including TMZ, resulting in an OS benefit for these patients [9]. Dunn et al showed that a greater extent of methylation was associated with significantly longer OS [10]. Other studies in anaplastic gliomas have shown that MGMT promoter methylation status did not only influence patient outcome after chemotherapy but also impacted outcome after radiotherapy and may therefore be prognostic rather than predictive [11]. In contrast, other studies revealed that MGMT promoter methylation was not associated with better OS and progression-free survival; both endpoints were comparable in patients with expressed MGMT and those with MGMT silencing. The studies by Costa et al. and Park et al. on glioblastoma patients treated with TMZ-based chemoradiation revealed that MGMT promoter methylation was not associated with improved outcome [12, 13]. Our study found that MGMT promoter methylation was not associated with a significant change in patient outcome. However, glioblastomas with unmethylated MGMT promoter, who received chemoradiotherapy mainly TMZ therapy, had a late tumor recurrence (Figure 2B; Table 3). Hence, MGMT promoter methylation in glioblastoma cannot be considered as a significant factor for long survival.

The relationships between IDH1 mutation and MGMT promoter methylation with the type of chemotherapies were also assessed independently with tumor recurrence interval. Our results found that glioblastoma cases, regardless of IDH1 status, that were treated with TMZ or TMZ and additional chemotherapeutic agents did not show any difference in tumor recurrence interval (Figure 3). This was completely different among cases in which MGMT methylation was the main independent factor. Although methylated MGMT promoter with IDH1 mutant glioblastoma cases showed clinically significant results, the cases with unmethylated MGMT promoter and IDH1 mutation treated with combined chemotherapies had significantly late tumor recurrence. These cases were mostly IDH1 mutant (Table 4). This means that glioblastoma with wildtype IDH1 and unmethylated MGMT promoter should be treated aggressively with combined chemotherapies (TMZ plus other chemotherapies) to improve overall survival. Two other studies also found conflicted findings. Combs et al. analyzed a group of 160 patients with glioblastoma treated with radiotherapy and TMZ for the impact of MGMT promoter methylation and IDH1 mutation. Unexpectedly, OS was no longer among the group of methylated MGMT promoter compared with patients without MGMT promoter methylation [17]. In contrast, Millward et al. demonstrated that the combination of methylated MGMT and IDH1 mutation was associated with considerably longer OS and PFS in a series of chemoradiotherapy-treated glioblastoma tumors [14]. Alassiri et al. also found a positive impact of both MGMT methylation and IDH1 mutation on the overall survival of Saudi patients with glioblastoma [18] but the study did not relate the findings with other treatment modalities. Another recent study by Pandith et al investigated the relationship between IDH1/IDH2 mutations and MGMT methylation in patients receiving chemotherapies in different types of malignant gliomas (astrocytomas and oligodendrogliomas). Compared to our study, the only treatment modality used in their study was TMZ chemotherapy while IDH1/2 sequencing was the primary method to detect mutation. Using IDH1/IDH2 sequencing from fresh tissue nowadays are somewhat difficult either because of limited facilities or because the high cost of sequencing [19]. Our results concluded that IDH1 mutation and MGMT gene promoter methylation are considered independent prognostic factors in glioblastoma. Although IDH1 mutant glioblastomas showed late tumor recurrence in patients younger than 50 years of age, the type of treatment modalities may not show additional beneficial outcome. Patients with unmethylated MGMT gene promoter with IDH1 mutation, treated with chemoradiotherapy including TMZ had a late tumor recurrence while glioblastomas with wildtype IDH1 and unmethylated MGMT gene promoter should be treated aggressively with radiotherapy and combined chemotherapies to delay tumor recurrence.

One limitation must be acknowledged in our study, that the total number of cases analyzed for MGMT promoter methylation and IDH1 mutation are low. Despite this limitation, our report is the first study in Saudi Arabia that correlates these molecular biomarkers with recurrence-free interval in totally resected glioblastomas, reflecting the impact of adjuvant therapies as well as the specific type of chemotherapies on patient outcome.

This is the first paper to describe the role of IDH1 mutation and MGMT promoter methylation status in terms of overall survival and recurrence-free survival by patients group treated with different therapeutical modalities in Saudi Arabia. The impact of IDH mutations and MGMT promoter methylation on OS and PFS is extensively described in the literature. Our results highlighted the impact of these molecular biomarkers on different treatment modalities including radiotherapy and chemotherapies on glioblastoma outcome. Additional molecular studies and raising the sample size could increase the value of the investigation.