Involvement of SVZ had been proved to be a prognostic factor for adult GBM in many researches [14–16, 18–21]. The clinical significance of this finding was to help us judge the prognosis of patients before surgery. On the one hand, several studies have reported the discovery of glioma stem cell in SVZ, where provides a protective environment and increase resistance to irradiation and chemotherapy [22–29]. On the other hand, tumor cells could shed into the lateral ventricle and spread with cerebrospinal fluid, resulting in poor progression free survival and overall survival. However, due to the rarity of pediatric glioblastoma, nearly all of the reports about SVZ were based on adult population in the past. The only report containing some cases of high-grade glioma in children found a poor prognosis for high-grade glioma patients with involvement of SVZ, suggesting that the prognosis of high-grade glioma patients with involvement of SVZ in children may be as poor as that of adults [15]. We are the first to research on the impact of tumor involved with SVZ on survival in children population. Our results indicated that involvement of SVZ is a prognostic factor for PFS and OS in pGBM independent of EOR and adjuvant therapy.
Researchers held different opinions on the relationship between SVZ involvement and total resection rate in the past reports [14, 21]. In order to avoid the risk of communicating hydrocephalus and the spread of tumor with cerebrospinal fluid caused by ventriculotomy, many neurosurgeons tend not to remove the entire tumor which involved lateral ventricle [30]. However, it had also been reported that surgical incision of lateral ventricle to achieve complete resection of supratentorial GBM has a better prognosis [31]. Our results confirmed that there was no relationship between GTR and involvement of SVZ, however, since GTR could prolong the survival of pGBM in our study, we advise to realize GTR with the application of microsurgical technology and intraoperative neuronavigation as far as possible even facing tumor involved with SVZ.
Adult GBM with no SVZ involvement were more likely to receive active adjuvant therapy in the literature [14], they attributed this difference to raised gumption for treatment given by mild symptoms (higher KPS) of patients, we also found active treatment were given to patients with no SVZ in pGBM cases, but our patients didn’t represent a serious condition when SVZ was involved.
Harat M et al. showed SVZ infiltration of GBM by O-(2-[18F] fluoroethyl)-L-tyrosine (FET) PET scan, they found SVZ infiltration was correlated to larger tumor volumes [32]. Our results also showed that supratentorial GBM with SVZ infiltration were larger in children. To some extent, tumor itself may not originated from SVZ, but invaded SVZ with its growth. This view was supported by the theory that tumor stem cells migrate along the CXCL12 / CXCR axis or pleiotrophin-driven axis to SVZ [33, 34]. According to our results, we could speculate that the same mechanism of glioma stem cell migration also exists in children.
Although it has been reported that the degree of PTBE is not related to tumor volume [35], however, surprisingly, we found that pGBM exposed to SVZ had lower edema index (EI), which may be related to the expression of aquaporins and tumor microenvironment, we hope the specific mechanism can be studied in future. Meanwhile, mild PTBE suggests that patients with SVZ involvement may needn’t to use steroids or mannitol before surgery to reduce tumor edema.
Status of IDH gene has been tested routinely in our center. Because of the low incidence of IDH gene mutation, relationship between IDH gene mutation and SVZ involvement cannot be analyzed properly. In consideration of it had been reported that IDH gene mutation is not associated with SVZ infiltration in adults GBM [25, 36], we need a larger sample size to confirm the result in pGBM. In addition, we found that there was no difference in the expression of ATRX and p53 between SVZ contact subset and no SVZ contact subset, which indicated that the poor prognosis caused by SVZ exposure was not related to these pathological prognostic indicators.
At present, no particular treatment was applied on GBM with SVZ involvement. In the retrospective analysis, whether patients can benefit from radiotherapy for SVZ is still controversial [37, 38]. A prospective study found that patients with radiation necrosis in SVZ have a longer survival time [39]. Several drug treatments are being studied, it had been reported that CXCL12 inhibitors can improve radiosensitivity and reduce tumor cell proliferation in animal models [33]. Besides, administration of drugs, vectors or cells in the lateral ventricles, which can bypass the blood-brain barrier, have been considered as a more effective treatment in theory, and obtained positive results in animal models [40–43]. Our study shows that RT + CT is still an effective therapy of pGBM, but the treatment of pGBM with SVZ infiltration needs further study in the future.