With the present survey, we aimed to obtain an overview of different therapeutic strategies in children and adolescents with recurrent/progressing pHGG across different European countries by interviewing experts in paediatric neuro-oncology on their advice in four real-world case scenarios chosen to represent routine treatment situations in pHGG.
Across the 22 European countries and all case scenarios, most respondents considered it important to include pHGG patients in phase I/II clinical trials at recurrence or progression. Currently, there are 56 ongoing early phase trials (mainly at US sites) including paediatric patients with recurrent/progressing HGG registered at ClinicalTrials.gov or the EU Clinical Trials Register, most of them focusing on targeted treatment or immunotherapeutic approaches (Supplementary Table S2). This reflects the vigorous worldwide efforts towards finding urgently needed innovative and effective treatment approaches in this desperate setting. It also exhibits the scientific and clinical willingness for cooperation, studying concerted treatment concepts rather than pursuing mere individual decisions and strategies.
Most survey participants intended oncological treatment in three out of four case scenarios, while in the case of a 17-year-old female with gliomatosis cerebri and marked symptoms, more than half of respondents chose palliative treatment/best supportive care, highlighting the importance of considering health condition in the therapy concept. The widespread intention observed in the present survey to continue oncological treatment of young patients facing the (except in case four) most likely palliative situation of recurrent/refractory HGG may also reflect the hope and strive of treating physicians to find an effective treatment in the near future. However, the real-life status quo of patients and their families often contrasts these efforts: Their needs and wishes are the mainstay of best supportive care, which should be addressed and planned early enough at disease recurrence/progression.
Maximal safe resection was consensually considered in only one case of localized hemispheric HGG. While extended resection is impossible in gliomas of the brainstem, basal ganglia and thalamus, a higher extent of resection is known to be a positive prognostic factor for survival in non-pontine pHGG at initial diagnosis.1,6,12 In a study by Ringel et al., gross total repeat resection conferred an increased overall survival in adult patients with recurrent glioblastoma.21 Biopsy has been shown to be feasible and has contributed especially to recent knowledge on the biology of DMG, and has therefore been recommended to gain information on potentially druggable targets whenever practicable.8,23,24
Throughout all case scenarios, radiotherapy was considered as a backbone of a multimodal relapse treatment, with most experts proposing local re-irradiation up to the maximal applicable dose in patients with localized supratentorial tumours, DMG, or gliomatosis cerebri. In a meta-analysis of therapeutic approaches spanning the past 20 years in paediatric patients with recurrent non-pontine HGG, Kline et al. found an overall survival of 14 months with local re-irradiation, which was longer than with other approaches.18 Re-irradiation with 30–54 Gy led to clinical and survival improvement in pHGG patients including DIPG, especially when the interval between the first and second irradiation was longer than one year.8,19,20,24,25 Although the role of craniospinal irradiation in disseminated disease remains unclear and haematological toxicity has to be expected, its feasibility has been reported.26 In the present survey, two thirds of experts recommended CSI (preferably after deferral through chemotherapy) in a young child with disseminated spinal cord infant HGG.
Systemic chemotherapy was chosen by up to three quarters of experts in non-DMG cases in the present survey, while it was regarded as promising by barely one third in DMG. Temozolomide was considered the first option for relapse treatment in one temozolomide-naïve case (Case 4). CCNU (either as monotherapy or in combination) was the preferred agent in patients who had already received initial radiochemotherapy with temozolomide. The addition of CCNU to temozolomide maintenance treatment improved survival in pHGG and CCNU is commonly used in adult patients with recurrent glioblastoma, limited however, by considerable haematological toxicity.6,27
Numerous combination chemotherapy strategies have been tested in patients with pHGG, lacking obvious survival advantages with any particular regimen, but yielding increased toxicity with intensified combinations.8,9,13,14,16,28−32 In the meta-analysis conducted by Kline et al., chemotherapy approaches showed an overall survival of only four months in paediatric patients with recurrent HGG.18
In selected young children with HGG, a first-line chemotherapy approach allows deferring or even avoiding radiotherapy and may therefore be preferred in “infant HGG”.11,33 The clinical impact of targeted therapy in case of, e.g., ALK, ROS or NTRK gene fusions is still subject of ongoing clinical studies. Despite reports of impressive clinical responses, the duration of tumour control and the best possible application mode and time point of these inhibitors in addition or as substitution for chemotherapy remain unclear.
Intraventricular chemotherapy was recommended as part of a systemic chemotherapy regimen or metronomic antiangiogenetic treatment concept by a quarter of respondents in Case 4 with disseminated spinal cord HGG.
More than ten percent of experts would add epigenetic modifier treatment with histone deacetylase (HDAC) inhibitors, e.g., valproic acid, which may sensitize HGG to radiochemotherapy. Retrospective analysis suggested better outcomes with valproic acid as antiepileptic treatment in pHGG patients including DIPG.17,34 A recent phase II study of valproate added to radiotherapy and bevacizumab in newly diagnosed pHGG observed tumour responses and indicated a survival benefit for patients with glioblastoma and constitutive mismatch repair deficiency, although in total, EFS and OS were not improved compared with historical data.10 In the ongoing HIT-HGG-2013 trial, valproate is added to radiotherapy and temozolomide in children and adolescents with HGG (EudraCT: 2013-004187-56).
Almost all European experts agreed on the importance of a molecular genetic workup to possibly identify alterations allowing for targeted treatment, which was regarded as mainstay of treatment in all cases in the present survey.
BRAF/MEK inhibition was the most popular targeted treatment option among survey participants. It has been reported to induce responses in BRAFV600E-mutated pHGG and is likely to be more effective in a combination regimen.1,33,35−37 The combination of dabrafenib and trametinib in children with recurrent/progressing HGG is currently being investigated in a phase II trial (NCT02684058; Supplementary Table S2).
Other targeted treatment options proposed in the present survey were EGFR-directed treatment (monoclonal antibody nimotuzumab or TKI erlotinib) in case of EGFR overexpression, CDK inhibitors in case of CDKN2A deletion and EZH inhibitors for H3K27M mutated DMG with SMARCB1 deletion.
Druggable targets can be found in a considerable proportion of patients with pHGG, and personalized treatment concepts may offer benefits for selected patients, where prolonged survival and tumour responses can be observed, even in DIPG.8,14,15,22,24,33,37−39 However, apart from high-priority targets such as BRAF-, ALK-, ROS- or NTRK-alterations, evidence is still limited for most therapeutic options. Although there is no clear survival advantage so far and the spectrum of potential targeting drugs crossing the blood-brain-barrier is narrow to date, most experts exhibited their expectations on targeted treatment in the present study.
The addition of the VEGF-directed monoclonal antibody bevacizumab to (radio-) chemotherapy showed some objective responses in a subset of paediatric HGG patients (e.g., with contrast-enhancing lesions more similar to “adult” patterns) but failed to improve survival, at the same time increasing toxicity.10,40−42 Nevertheless, adult data show that the addition of bevacizumab in recurrent glioblastoma can yield a survival benefit, may spare steroids and stabilize the clinical status for a longer time due to its anti-oedematous effect, and, despite its toxicity, has no negative effect on quality of life.43 This may be reflected in the recommendations by paediatric neurooncologists in the present survey study, where bevacizumab was chosen by twelve percent of respondents.
Immunotherapeutic approaches were considered by a significant proportion of respondents only in Case 1 of the present survey, and their selection would depend on the availability of clinical trials. This was also reflected by a significant difference in proposing immunotherapy concepts between experts from other European countries and those from Germany, where trials combining metronomic cyclophosphamide and dendritic cell vaccination with checkpoint blockade (nivolumab/ipilimumab) for relapsed HGG (HIT-Rez-Immunovac, NCT03879512, Supplementary Table S2) or checkpoint inhibition (nivolumab) with entinostat in relapsed malignancies (INFORM2-NivEnt, NCT03838042) are currently recruiting.
While, generally, paediatric tumours show a low tumour mutational burden (TMB), limiting efficacy of checkpoint inhibitors, sustained responses were observed in some pHGG patients with germline mismatch repair deficiency or high TMB, especially when using a combined approach.2,15,37,44 Interim results of the ongoing HIT-Rez-Immunovac trial were promising, but current vaccination strategies require (near) total resection and still lack a clear survival benefit compared to re-irradiation in adults with relapsed HGG.45,46 Anti-GD2-directed CAR-T cell application for DMG may be another future option, and local delivery of HER2-directed CAR-T cells is currently being tested in children with refractory/relapsed CNS tumours (BrainChild-01, NCT0350099).15,47 Yet, novel immunotherapeutic approaches still face challenges with crossing the blood-brain-barrier, low mutational burden, tumour heterogeneity, immunological “cold” tumours, and antigen escape.15
Tumour-treating fields (TTF), chosen by a quarter of respondents in Case 1, yielded improved survival when combined with temozolomide maintenance in adult glioblastoma patients.48 Despite toils like its long daily application time, TTF was reported to be feasible and well-tolerated even in young paediatric patients,49,50 and is subject of ongoing trials (see Supplementary Table S2).
Our survey implied some limitations by predefining answers, which may have simplified the clinical decision-making. To allow more individualized treatment options, additional free-text options were used but the analysis for the free text statement was difficult and may be hampered and potentially biased by our attempts to categorize them for comparison and interpretation reasons. Moreover, the respondents had to rely only on the information provided in the case descriptions, without the opportunity for additional information and/or discussion with colleagues. Decision-making might have been easier if we had provided imaging or detailed radio-morphologic descriptions to obtain an additional visual impression or rule out signs of pseudo-progression, for example. However, the real-world case scenarios were all centrally reviewed by neuroradiologists; thus, pseudo-progression was ruled out, and the possibility of an underlying pseudo-progression was no point of interest for the present study. Furthermore, treatment decisions may have been influenced by the availability of certain treatment modalities in the respective countries and some might also have been based on personal opinions and preferences as well as previous experiences. However, it was not the goal of this study to evaluate medical evidence for the therapeutic strategies chosen by the respondents.
Nevertheless, the high number of respondents certainly highlights an overall need for sharing expertise in the desperate setting of treating young patients with relapsed/refractory HGG and discussing treatment decisions.
The fact that all respondents came from European countries being embedded in the SIOPE-BTG network, working in similar professional settings, most of them with a professional experience of more than ten years, enabled comparable and meaningful results to at least identify general tendencies for decision making in such difficult, highly individualized treatment situations.