The diagnosis of GBM confers a dismal prognosis, with a median OS of only 14 to 18 months even with standard treatment. Efforts at improving OS have had only modest success. In-field or marginal recurrences after RT are common, leading to the assumption that outcomes will be improved if we could find an agent sensitizing GBM cells to RT. Many recent in vitro and in vivo evidences has emerged indicating that AEDs may act synergistically with RT, moreover, AEDs may have anti-tumor effects themselves. VPA is the drug being discussed most frequently, and it is an antiepileptic agent with histone deacetylase inhibitor (HDACi) activity shown to sensitize GBM cells in preclinical models, to promote hyperacetylation of DNA-binding histone proteins together with decondensation of chromatin, and to induce a demethylation/activation process of tumor suppressor genes. However, these results are not universal and have been the subject of much debate.
In our study, the inferior OS was observed in the AED group and in the subgroup of VPA. This detrimental effect seemed to be evident in male and in younger patients. Regarding age, those younger than 40 years old had a trend of higher risk of death in the AED group compared to the non-AED group, while the HR for death was significantly higher for those younger than 65 years old in the subgroup of VPA. (Table 3) The underlying cause of these differences remains unclear. In the literature review, results of clinical studies are inconsistent as well. A single arm phase II study enrolled 37 patients with GBM, receiving VPA, 25 mg/kg orally, divided into 2 daily doses concurrent with RT and TMZ. It was inspiring that the median OS reached 29.6 months, and median PFS was 10.5 months [12]. A retrospective analysis of 544 patients from Memorial Sloan-Kettering Cancer center showed that VPA use during RT was associated with improved OS. Patients with AEDs for more than half the duration of RT were enrolled. Of the 5 most common AEDs during RT, only VPA was associated with significantly improved OS (HR 0.67, p = 0.047). When the analysis was restricted to those receiving concurrent TMZ, VPA use was marginally associated with better OS (HR 0.54, p = 0.057). The results implied that HDAC inhibitors, like VPA, may enhance the effect of RT and should be subjected to future clinical trials [14]. An assessment of the impact of the interaction between AED use and CCRT on survival was performed in the European Organization for Research and Treatment of Cancer/ National Cancer Institute of Canada (EORTC/ NCIC) TMZ trial, and it showed prolonged survival with VPA use [15]. Nevertheless, a combined analysis of four contemporary randomized trials with individual patient information offered a different perspective. They evaluated PFS and OS between two conditions: any VPA or LEV use and no use at baseline, or VPA or LEV use both at start of and still after CCRT. The authors concluded that VPA or LEV use was not beneficial, and did not being justified for reasons other than seizure control outside clinical trials [13].
An unresolved issue is that whether the positive effect of VPA occurs only in patients undergoing RT without TMZ? The phase II study mentioned before included a small number of patients and there was no control arm. Although all of the 37 patients planned to be treated with concomitant RT/TMZ, there were 8 patients (21.6%) stopped TMZ mainly due to bone marrow suppression [12]. The study from MSKCC enrolled patients between 1998 and 2008, and only about one-third of this cohort (34.8%) had taken TMZ during RT [14]. So their result must be interpreted carefully. In the pooled analysis of AVAGlio, CENTRIC, CORE, and RTOG 0825, the patient data were obtained from TMZ-containing arms of the four trials. They indicated that the OS was not improved with VPA use both at baseline (HR 0.96, p = 0.633) and at start of and still after CCRT (HR 1.10, p = 0.44) [13]. One of the advantages of our study is that all subjects received the standard treatment of concomitant RT/TMZ and adjuvant TMZ; therefore we made a greater contribution to current clinical practice compared to previous publications. The interaction between VPA and TMZ has not been fully understood. Although many retrospective series indicated VPA use might be associated with improved survival, publication bias inevitably occurred. To date, there is no randomized data to illustrate this issue. Our result discouraged the routine use of VPA during RT/TMZ.
With regard to LEV, our data showed there was a trend to be worse when LEV being prescribed during RT/TMZ (HR 1.18, p = 0.079), furthermore, it seemed to be more harmful in female (HR 1.34, p = 0.06). Notably, male had significantly higher risk of death in the subgroup of VPA (HR 1.47, p < 0.0001) (Table 3). Another retrospective, single-center study reported different conclusion about LEV. 418 patients were treated per the current protocol and all used at least one AED. A total of nine AEDs were evaluated, and the three most common drugs are LEV, VPA, and gabapentin. The significant benefit existed only in patients with LEV compared to those without it (median OS: 21 versus 16 months, p < 0.001). To go a step further, the positive impact of LEV on OS was seen in the group with a methylated MGMT promoter (HR 0.174, p = 0.006), but not in the unmethylated group (p = 0.623). In addition, the median OS in patients with VPA was shorter than those without VPA (18 vs 20 months, p = 0.38) [16]. Although the difference was not statistically significant, the adverse effect of VPA on OS was consistent with our work. Our result still did not show the benefit of LEV during RT/TMZ.
Likewise, the results of pre-clinical studies were also controversial. Eui Kyu Chie et al demonstrated evident radiosensitizing effect for fractionated RT of VPA in tumor bearing mice with two different cell lines [9]. Dinesh Thotala et al revealed that VPA led to significant tumor growth delay and radiosensitization with survival benefit, inhibition of cancer cell proliferation, cell cycle arrest, and accumulation at G2/M [10]. Zhiying Li et al reported survival rate in human glioma cell populations exposed to VPA + TMZ or ACNU was significantly decreased compared with that of the TMZ or ACNU alone groups. VPA not only enhanced the inhibitory effects of TMZ and ACNU but also induced tumor apoptosis [17]. However, there are researchers holding the converse opinion. A study from Germany used three GBM cell lines and primary spheroid cultures to evaluate the effect of VPA, and did not suggest a radio-sensitizing effect of VPA in general at concentrations achieved in the clinical situation. They also observed VPA-mediated acceleration of GBM cell migration which might boost tumor spreading and brain infiltration [11].
Another issue worthy of discussion is that the prognostic value of epilepsy in patients with GBM. An incidence of epilepsy was in the range of 25–60% in the literature. Some authors believed that epileptogenic GBM convey a favorable outcome, which might be due to early diagnosis [18–20]. But there are still other studies referring that epilepsy at presentation is not an independent prognostic factor for longer survival [21]. Additionally, Sharon Berendsen et al reported that for those who presented with epilepsy, the use of VPA did not associate with survival [18]. The aim of AED use is therapeutic or prophylactic may play a role in outcomes. Anticonvulsant prophylaxis is not recommended in patients with newly diagnosed primary or secondary brain tumors, especially in light of a significant risk of serious adverse events and problematic drug interactions. The incidence of anticonvulsant side effects appears to be higher (20 to 40%) in brain tumor patients than in general population. This increment is due at least in part to the additive or synergistic effects of concurrently administered drugs (especially chemotherapeutic agents) and to the underlying brain tumors [22, 23]. In our study population, there are more people in the AED group had the drug history of anti-convulsants before GBM diagnosis than in the non-AED group (22.6% versus 18.1%, p = 0.078), and these patients had poorer outcome (HR for death 1.211, p = 0.019). The superiority of our study is that we adjusted for past history of AED use as a potential confounding factor of survival.
There are some disadvantages in our study. First, the genetic alterations of O6-methylguanine–DNA methyltransferase (MGMT) promoter methylation status and isocitrate dehydrogenase mutations were not available in the NHIRD. Second, other factors associated with OS such as patient performance status, Recursive Partitioning Analysis classes, and clinic-pathological parameters (eg. extent of initial resection, tumor location, and number of lesions) were not analyzed due to the limitation of database.
In order to overcome these shortcomings, we performed sensitivity analyses to simulate the distribution of IDH1 mutation and methylation status of MGMT in our cohort. Comprehensive literature review was performed, especially focusing on data in eastern countries. Approximately, the incidences of IDH1 mutation and MGMT promotor methylation are 15% and 40%, and the HRs of OS are 0.46 and 0.57, respectively [24–30]. We used these assumptions and incorporated status of IDH1 and MGMT promotor into multi-variate Cox regression model. Regarding extent of resection, we believed that subtotal resection is correlated with tumor size. Hence, surgical treatment codes according to tumor size were analyzed to evaluate the impact of margin status on our findings. The same conclusion was drawn by the sensitivity analyses (Additional Table 2). The detrimental effects of AED overall and of valproic acid still existed with adjustment for IDH1, MGMT, or tumor size.