The molecular markers of CD34 and BRAFV600E mutation are frequently met in GNT [4-7]. Although a few of pediatric gliomas share these molecular features with GNT [3, 5, 10], CD34 expression and BRAFV600E mutation, as an adjunct diagnostic marker, are routinely screened in the diagnosis of GNT [5-7].
The frequency of CD34 expression and BRAFV600E mutation in GNT
As a molecular marker of progenitor cells, CD34 often expresses in low-grade or developmental brain tumors, which are usually accompanied by chronic epilepsy, such as the so-called “low-grade epilepsy-associated neuroepithelial tumors (LEAT)”, but none of normal adult or developing human brain and tumors without epilepsy are CD34 positive [3-5, 8, 18]. GNT, as the most common tumor type in patients with epilepsy, are also frequently reported with CD34 expression, approximately 50-60% [3, 4]. In particular, the ratio of CD34 expression was often higher in GG than DNT [3, 5]. For example, Giulioni M, et al. exclusively observed the CD34 expression in low-grade epilepsy-associated tumors (n = 187), and found 54.1% of CD34 positive in GNT, with a higher expression of CD34 in GG than DNT (74.7% vs. 23.5%) [3]. In our study, we reviewed the CD34 expression in GNT with epilepsy and found 80.2% of tumors were CD34 positive. Also, the ratio of CD34 expression in GG was significantly higher than DNT (87.9% vs. 36.8%; P < 0.001), which was line with the previous studies [3, 4, 18].
The BRAFV600E mutations that were primarily found in melanomas also occur in brain tumors, which, similar to CD34, mainly affect low-grade glial or glioneuronal tumors, such as GG, DNT, and PA, as well as pediatric PXA and diffuse astrocytoma [6, 7, 11]. The mutation of BRAFV600E in GNT was reported ranging from 20% to 60% [6, 7, 19]. In present study, tumors with BRAFV600E mutation were detected by IHC in 57.8% (59/102) of GNT, including 61.4% of GG, 38.5% of DNT and 50% of mixed GNT, but no difference of BRAFV600E mutation was found between GG and DNT (P = 0.118). Similarly, higher rates of BRAFV600E mutation are often met in GG than DNT, but less statistic differences were recorded between two types of tumors [7, 17, 18, 20].
The clinicopathological features of CD34 expression
The relationship between clinicopathology and CD34 expression in GNT has been studied in some studies, but the results were always inconsistent or with limited cases [3-5, 19].
For demographic features, Blümcke I, et al. found patients with brain tumors with epilepsy and CD34 expression had younger age at seizure onset or at surgery [5]. And Vornetti G, et al. found CD34 expression in LEAT was significantly associated with a longer duration of epilepsy [19], which was similarly reported by Giulioni M, et al. who also reported that CD34 expression in LEAT appeared to be significantly related to older age at surgery, higher AED intake, and female sex by univariate analysis [3]. In present study, we found GNT with CD34 expression occurred more in adults than children (OR = 2.5, P = 0.014), and CD34 expression was also associated with longer duration of epilepsy (P = 0.027) and drug-resistant epilepsy (P = 0.036) by univariate analysis.
The tumor or pathological characteristics were less reported to be related to GNT with CD34 expression, except that Lisievici AC, et al. found CD34 expression in GG was more in temporal lobe [21]. In present study, we also found GNT with CD34 expression were more occurring in temporal than non-temporal sites (P = 0.007) by univariate analysis.
Although CD34 expression tends to occur in lesions with epilepsy, the seizure semiology or EEG finding is seldom reported to be related to GNT with CD34 expression [3, 21]. In present study, however, we found patients with CD34 expression in GNT had more tendency of experiencing seizure aura (P = 0.007) and concordant EEG findings (P = 0.032) than those without CD34 expression by univariate analysis.
The clinicopathological features of BRAFV600E mutation
Although the BRAFV600E somatic mutation in neuronal linage cells (or glial lineage cells) was proved to play a key role in epileptogenic properties (or tumorigenic properties) of GG [22], the relationships between clinicopathological features and BRAFV600E mutations in GNT were not well studied or with less data [6, 16, 17, 19, 20, 23].
Several demographic features were reported to be related to GNT with BRAFV600E mutation, including younger age at surgery for GG (P = 0.005) [23], younger age of seizure onset for epilepsy-associated brain tumors (P = 0.020) [6], and female patients for GNT with epilepsy (P = 0.022) [17]. However, Schindler G, et al. noted no significant differences of patient age at surgery for GG with BRAFV600E mutation [7]; Zhang YX, et al. reported no significant correlation between the BRAF status in GNT and age at surgery, as well as age of seizure onset and duration of epilepsy [17]; and Xing H, et al. also didn’t find brain tumors with epilepsy and BRAFV600E mutation were associated with gender and duration of epilepsy [6]. In present study, we didn’t find any associations of BRAFV600E mutation in GNT with age of seizure onset, duration of epilepsy and patient gender, except for the older age at surgery (P = 0.015).
For tumor or pathological characteristics, Schindler G, et al. found GG with BRAFV600E mutation were more in temporal lobe [7]. Prabowo AS, et al. found in both GG and DNT, the presence of BRAFV600E mutation was significantly associated with the expression of CD34 [20]. Vornetti G, et al. found BRAF mutation in LEAT was predominant in right-sided lesions [19]. However, Koelsche C, et al. found CD34 was not differentially expressed in BRAF wild-type and -mutated tumors of GG [23], and Xing H, et al. found there was no statistical difference between BRAFV600E mutations and wild type for tumor site [6]. Also, we didn’t find GNT with BRAFV600E mutation were associated CD34 expression, tumor locations, calcification or encystation, et al.
With respect to seizure semiology or EEG findings, BRAFV600E-mutated LEAT [19], as well as GNT [17], were reported to be with more seizure types. However, we didn’t find GNT with BRAFV600E mutation were associated seizure semiology, except that the concordance of EEG findings was different (discordant vs. concordant, P = 0.031) by univariate analysis.
Seizure outcomes and tumor recurrence
The correlations between CD34 expression or BRAFV600E mutation in GNT and postoperative seizure outcomes have been evaluated in previous studies [20, 24, 25], but they were always with negative results [6, 17, 19]. For example, Wang Y, et al. found 9 patients with GG had postoperative seizure recurrence, and 8 of them were immunoreactive for CD34 [24], and Prabowo AS, et al. found the expression of BRAFV600E in GNT was associated with a worse postoperative seizure outcome [20]. However, Vornetti G, et al. didn’t find LEAT with BRAFV600E mutation or CD34 expression were associated with seizure outcomes [19]. Zhang YX, et al. didn’t find any significant correlations between the BRAF status in GNT and postoperative seizure freedom [17]. Also, Xing H, et al. reported there was no statistical difference of epilepsy-associated brain tumors between BRAFV600E mutations and wild type in Engel outcome comparison [6]. Similarly, we defined no differences between CD34 expression (P = 0.807) or BRAFV600E mutation (P = 0.937) in GNT and postoperative seizure outcomes.
The GNT are benign, slow-growing tumors, and patients with GNT rarely experience tumor progression or recurrence, although 5% (or less) of GG (nearly 0% of DNT) with anaplasia or malignant progression were reported in previous studies [1, 26]. During the whole follow-up period of 54 months (IQR: 26-78 months) in our study, 6 patients had tumor recurrence (GG/5 and DNT/1) and 2 cases of GG had malignant progression, with the 10-year tumor PFS reaching 95%. Through univariate Cox regression analysis, we found the history of GTCS (HR = 0.12, P = 0.035), drug-resistant epilepsy (HR = 0.13, P = 0.030) and concordant interictal EEG findings (unknown vs. concordant; HR = 8.01, P = 0.039) were associated with longer PFS, but only the drug-resistant epilepsy was significant in the multivariate Cox regression analysis. In particular, when compared the Kaplan Meier curves between two groups [tumor with CD34 (+) vs. CD34 (-)] or groups [tumor with BRAF (+) vs. BRAF (-)], no difference was found in patients with detection of CD34 expression or BRAFV600E mutation.
The relationship of CD34 expression or BRAFV600E mutation in GNT with tumor survival (PFS or overall survival) have been studied, previously [16, 18, 21, 26, 27]. Although some of studies reported the significant correlation of CD34 expression or BRAFV600E mutation in GNT with tumor recurrence or progression [21], the extent of the surgical resection (or tumor location), instead of CD34 expression and BRAFV600E mutation, may play an important role of the tumor prognosis of low-grade GNT [16, 18, 24, 26]. However, when analyzing the association of tumor recurrence with resection extent or tumor locations, we didn’t find any statistic differences in resection extent (P = 0.833) and tumor locations (temporal vs. non-temporal, P = 0.498), which may be partly attributed to the high rate of complete tumor resection (99.2%) in our surgical cohort.