https://orcid.org/0000-0002-7242-0528
Abstract
Histone mutant gliomas (HMG) with histone H3 K27 and G34 mutations are recognized as biologically discrete entities with distinct anatomical locations, younger age at presentation (in comparison to the most common high-grade gliomas, IDH wildtype glioblastoma), and poor prognosis. There is a paucity of data regarding the management of adult HMG patients and no consensus on management. This study aims to identify current patterns of Australian and US neuro-oncology clinical practice for this entity.
Following institutional approvals, patterns of care questionnaire designed to capture relevant clinical variables was circulated through the Cooperative Trials Group for Neuro-Oncology (COGNO) in Australia and the Caris Precision Oncology Alliance in the United States (US).
Between 4/2021 and 10/2021, 43 responses were collected. 33% (n = 14) of responders tested all patients for HMGs routinely; 40.92% (n = 18) tested in select patients 26% (n = 11) did not test for HMGs. The common indications for testing selected patients were midline anatomic location (n = 18) and age (n = 11) (<50 years). 23 used molecular sequencing, 22 used IHC at their centers. Nine participants stated knowledge of histone H3 mutations did not affect their management of these gliomas, 11 said it affected their management at the time of recurrence, 23 stated it affected the management of midline K27M patients, 11 participants stated it affected the management of K27M mutant gliomas in other locations, and 3 felt it affected the management of G34R/V mutant gliomas.
Here we present a description of how the discovery of a new molecular subtype of primary glial tumors, histone mutated gliomas in adults, is being introduced into clinical practice.
Histone mutant gliomas (HMG) with histone H3 K27 and G34 mutations are diffusely infiltrating gliomas that display distinct molecular signatures, varied histopathological characteristics, anatomic preferences, and clinical behavior as compared to histone-wildtype glioblastomas. First described in diffuse intrinsic pontine glioma (DIPG), H3 K27M mutations are now recognized in other midline structures such as the thalamus, basal ganglia, and spinal cord; these are now termed diffuse midline glioma (DMG).1 The presence of H3 K27 mutations in nonmidline gliomas is rarely reported but not confer as dismal a prognosis and is not considered DMG.2 HMGs additionally include those with H3 G34 mutations, which are found exclusively in the cerebral hemispheres.3
H3 K27-altered DMGs are characterized by loss of H3 K27 trimethylation.4–7 Similarly, G34 mutations in H3F3A result in hypomethylation of the nearby K37 site and drive downstream oncogenic changes.8 This group is also now newly described in the WHO Classification of Tumours of the Central Nervous System, referred to as diffuse hemispheric gliomas, H3 G34-mutant.1
Adult HMGs have a poor prognosis and a younger age of presentation compared to histone wildtype adult gliomas (median overall survival of 19.6 months and age of onset of 32 years for adult K27M mutant gliomas and 12.4 months and 25 years for G34 mutant gliomas respectively). For comparison, the more common high-grade glioma in this age group (IDH-mutant grade 4 astrocytoma) has an overall survival of 31 months.3,9,10
Gliomas with histone H3 K27 and G34 mutations may be diagnosed by molecular sequencing. Immunohistochemistry (IHC) can also be used to diagnose K27M mutations directly (specificity and sensitivity 100%), supported by the loss of K27 trimethylation (K27me3) (specificity 98%, sensitivity 100%).11 Although IHC to specific G34 mutations has also been developed, recent data has shown high rates of false negatives and positives, leading to a preference for diagnosis by molecular sequencing.12 Other molecular features are associated with the presence of K27M and G34 mutations and can be used as indicators for NGS testing for histone mutations. For example, these tumours are universally IDH-wildtype, and most are MGMT promoter unmethylated.13–16
DMGs have been well studied in the pediatric population with multiple studies failing to demonstrate clinical benefit from systemic therapies.17,18 However, there is much less information about DMGs and other HMGs in the adult population, where reported differences in anatomic preferences and clinical behavior suggest the potential for distinct etiopathology from their pediatric counterparts.9,13,19 Given these differences, it is not clear if the results of pediatric DMG clinical trials may be extrapolated to adult HMGs. However, there remains a paucity of data regarding the management of adult HMG patients and there is no published consensus for pathologic testing or management. In the absence of clear literature guidance on how best to treat these patients, we sought to survey the broad neuro-oncology community regarding patterns of care to understand current practice trends for the diagnosis and management of HMGs. We hope that such information will be useful for future clinical trial design and practice guidelines.
Materials and Methods
A tailored online REDCap based survey was designed and approved by institutional review boards. The survey questionnaire targeted clinicians treating adult brain tumors and framed questions as a “snap shot” of current practice. Study data were collected and managed using REDCap electronic data capture tools hosted at Northern Sydney Local Health District and Duke University.20,21 Respondents were asked to identify their country of residence, institution of practice, and specialty, and were offered group authorship for participation. Respondents were deemed to practice in high volume centers if their place of practice was a known referral centre for neuro-oncology patients (as assessed by the authors). Questions were aimed at assessing the participants’ exposure to HMGs, testing practices, and management approaches. Responding clinicians could provide free-text comments about their experience managing HMGs. The surveys were circulated through COGNO in Australia and the Caris Precision Oncology Alliance membership in the USA. Clinicians with known neuro-oncology experience were additionally invited to participate via directed email.
Results
Between April 2021 and October 2021, surveys were circulated to clinicians registered with CARIS POA or COGNO (64 and 417 clinicians respectively) and 32 clinicians were directly emailed. 43 responses were collected in total, responses from POA, COGNO and directed emails were n = 8 (response rate 13%), n = 24 (6%), email n = 11 (34%) respectively. Respondents were distributed over 5 countries (Australia 51.2%, USA 39.5%, New Zealand 4.7%, India 2.3%, and Hong Kong 2.3%). 76.7% (n = 33) were medical oncologists, 13.6% (n = 6) were radiation oncologists and 9% (n = 4) were neurosurgeons. Of the 38 who agreed to be identified, 97% (n = 37) worked in high volume centers. We noted a total of 31 different centers of practice in total, 97% (n = 30) of which were high volume neuro-oncology centers. 14 out of the 31 centers directly treated pediatric patients or collaborated with pediatric centers in addition to treating adult patients.
Diagnostic Trends
33% (n = 14) of respondents tested all glioma patients for histone H3 mutations routinely, 42% (n = 18) tested in selected patients, and 26% (n = 11) did not test for HMGs (Figure 1a). Out of those who tested for HMGs in any instance there was a total of 25 different centers, 96% (n = 24) of which were high volume. Participants who tested in selected patients were then asked to select which indications they used for testing (age, anatomic location, imaging results, histopathology result, other). Each selection was accompanied with free text description of the factors they consider in each indication. The common indications for testing selected patients were anatomic location (n=18) (all participants described the main anatomical factor as midline location), age (n=11) (the majority described the main factor as younger patients or listed age ranges mostly less than 50 years of age), and initial histopathology (n = 9) (the most common histopathologic factor being IDH-wildtype by IHC) (see Figure 1b and 1c).
a. Pie Chart of Participants Who Routinely, Selectively or Do Not Test for HMG. b. Number of Participants Who Selected Each Individual Factor. c. Shows Combinations of Testing Factors Considered by Those Who Selectively Test for HMGs.
When looking at the total indications selected per participant the following combinations were seen: age, anatomical location, and histopathological features (n = 7), anatomic location alone (n = 5), age and anatomic location (n = 4), and age and histopathological features (n = 2).
23 Participants used molecular sequencing (targeted gene panel n = 20, whole exome sequencing (WES) n = 4, whole genome sequencing (WGS) n = 3, methylation profiling = 0), 15 participants used K27M IHC as the only IHC method, 1 used only K27me3 IHC and 6 used both K27M and K27me3 IHC.
Nine participants stated that knowledge of histone H3 mutation did not affect management while 11 reported that this knowledge affected management only on recurrence. 23 respondents stated that it affected the management of midline K27 patients, 11 stated it affected management of K27 mutant gliomas in other locations and 3 felt it affected management of G34 mutant gliomas. 95.3% (n = 41) used the Stupp et al protocol as first line treatment of midline K27 gliomas (with 85.3% of these saying it is used “always” or “usually”). Other first line treatments included clinical trial (n = 8), non-Stupp et al radiotherapy and temozolomide (n = 4 – most common regimen describe was RT followed by sequential temozolomide), radiotherapy only (n = 3), best supportive care (n = 3), and other (n = 1). The most common choices for management after recurrence were “other” (combination of bevacizumab, temozolomide, lomustine, procarbazine, vincristine, carboplatin, re-resection, and radiotherapy) (n = 24), temozolomide only (n = 13), clinical trials (n = 18, mostly “sometimes”), best supportive care (n = 14), and single agent temozolomide (n = 15). Reported management for nonmidline K27 gliomas and G34 gliomas were also similar (see Table 1).
Respondent-selected Treatment Regimens Used for HMGs in the Initial and Recurrent Setting
| BSC | RT Alone | TMZ Alone | RT+TMZ – Stupp Protocol | RT+TMZ – Other Protocol | Clinical Trials | Other | |
|---|---|---|---|---|---|---|---|
| MidlineK27Mglioma – initial | 3 (6.9%) | 2 (4.7%) | 1 (2.3%) | 41 (95.3%) | 4 (9.3%) | 8 (18.6%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Sometimes | Sometimes | Usually | |
| Midline K27M glioma – recurrent | 14 (32.6%) | 7 (16.3%) | 15 (34.9%) | 1 (2.3%) | 0 | 18 (41.9%) | 24 (55.8%) |
| Sometimes | Sometimes | Sometimes | Usually | Sometimes | Sometimes | ||
| Nonmidline K27Mglioma – initial | 3(7.0%) | 4 (9.3%) | 2 (4.7%) | 39 (90.7%) | 6 (13.0%) | 3 (7.0%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Usually | Sometimes | Not stated | |
| Nonmidline K27M glioma – recurrent | 14 (32.6%) | 10 (23.3%) | 15 (34.9%) | 0 | 1 (2.3%) | 12 (27.9%) | 20 (46.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Usually | ||
| G34R/V glioma – initial | 3 (7.0%) | 3 (7.0%) | 1 (2.3%) | 37 (86%) | 3 (7.0%) | 1(2.3%) | 3 (7.0%) |
| Rarely | Sometimes | Not stated | Usually | Sometimes | Not stated | 1 Each – Always/rarely/ usually | |
| G34R/V glioma – recurrent | 13 (30.2%) | 8 (18.6%) | 14 (32.6%) | 2 (4.7%) | 1 (2.3%) | 9 (20.9%) | 23 (53.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Sometimes/ Usually | Sometimes/Usually |
| BSC | RT Alone | TMZ Alone | RT+TMZ – Stupp Protocol | RT+TMZ – Other Protocol | Clinical Trials | Other | |
|---|---|---|---|---|---|---|---|
| MidlineK27Mglioma – initial | 3 (6.9%) | 2 (4.7%) | 1 (2.3%) | 41 (95.3%) | 4 (9.3%) | 8 (18.6%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Sometimes | Sometimes | Usually | |
| Midline K27M glioma – recurrent | 14 (32.6%) | 7 (16.3%) | 15 (34.9%) | 1 (2.3%) | 0 | 18 (41.9%) | 24 (55.8%) |
| Sometimes | Sometimes | Sometimes | Usually | Sometimes | Sometimes | ||
| Nonmidline K27Mglioma – initial | 3(7.0%) | 4 (9.3%) | 2 (4.7%) | 39 (90.7%) | 6 (13.0%) | 3 (7.0%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Usually | Sometimes | Not stated | |
| Nonmidline K27M glioma – recurrent | 14 (32.6%) | 10 (23.3%) | 15 (34.9%) | 0 | 1 (2.3%) | 12 (27.9%) | 20 (46.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Usually | ||
| G34R/V glioma – initial | 3 (7.0%) | 3 (7.0%) | 1 (2.3%) | 37 (86%) | 3 (7.0%) | 1(2.3%) | 3 (7.0%) |
| Rarely | Sometimes | Not stated | Usually | Sometimes | Not stated | 1 Each – Always/rarely/ usually | |
| G34R/V glioma – recurrent | 13 (30.2%) | 8 (18.6%) | 14 (32.6%) | 2 (4.7%) | 1 (2.3%) | 9 (20.9%) | 23 (53.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Sometimes/ Usually | Sometimes/Usually |
The number of respondents selecting each regimen and the most common frequency selected (rarely, sometimes, usually) are shown.
Respondent-selected Treatment Regimens Used for HMGs in the Initial and Recurrent Setting
| BSC | RT Alone | TMZ Alone | RT+TMZ – Stupp Protocol | RT+TMZ – Other Protocol | Clinical Trials | Other | |
|---|---|---|---|---|---|---|---|
| MidlineK27Mglioma – initial | 3 (6.9%) | 2 (4.7%) | 1 (2.3%) | 41 (95.3%) | 4 (9.3%) | 8 (18.6%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Sometimes | Sometimes | Usually | |
| Midline K27M glioma – recurrent | 14 (32.6%) | 7 (16.3%) | 15 (34.9%) | 1 (2.3%) | 0 | 18 (41.9%) | 24 (55.8%) |
| Sometimes | Sometimes | Sometimes | Usually | Sometimes | Sometimes | ||
| Nonmidline K27Mglioma – initial | 3(7.0%) | 4 (9.3%) | 2 (4.7%) | 39 (90.7%) | 6 (13.0%) | 3 (7.0%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Usually | Sometimes | Not stated | |
| Nonmidline K27M glioma – recurrent | 14 (32.6%) | 10 (23.3%) | 15 (34.9%) | 0 | 1 (2.3%) | 12 (27.9%) | 20 (46.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Usually | ||
| G34R/V glioma – initial | 3 (7.0%) | 3 (7.0%) | 1 (2.3%) | 37 (86%) | 3 (7.0%) | 1(2.3%) | 3 (7.0%) |
| Rarely | Sometimes | Not stated | Usually | Sometimes | Not stated | 1 Each – Always/rarely/ usually | |
| G34R/V glioma – recurrent | 13 (30.2%) | 8 (18.6%) | 14 (32.6%) | 2 (4.7%) | 1 (2.3%) | 9 (20.9%) | 23 (53.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Sometimes/ Usually | Sometimes/Usually |
| BSC | RT Alone | TMZ Alone | RT+TMZ – Stupp Protocol | RT+TMZ – Other Protocol | Clinical Trials | Other | |
|---|---|---|---|---|---|---|---|
| MidlineK27Mglioma – initial | 3 (6.9%) | 2 (4.7%) | 1 (2.3%) | 41 (95.3%) | 4 (9.3%) | 8 (18.6%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Sometimes | Sometimes | Usually | |
| Midline K27M glioma – recurrent | 14 (32.6%) | 7 (16.3%) | 15 (34.9%) | 1 (2.3%) | 0 | 18 (41.9%) | 24 (55.8%) |
| Sometimes | Sometimes | Sometimes | Usually | Sometimes | Sometimes | ||
| Nonmidline K27Mglioma – initial | 3(7.0%) | 4 (9.3%) | 2 (4.7%) | 39 (90.7%) | 6 (13.0%) | 3 (7.0%) | 1 (2.3%) |
| Rarely | Sometimes | Sometimes | Usually | Usually | Sometimes | Not stated | |
| Nonmidline K27M glioma – recurrent | 14 (32.6%) | 10 (23.3%) | 15 (34.9%) | 0 | 1 (2.3%) | 12 (27.9%) | 20 (46.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Usually | ||
| G34R/V glioma – initial | 3 (7.0%) | 3 (7.0%) | 1 (2.3%) | 37 (86%) | 3 (7.0%) | 1(2.3%) | 3 (7.0%) |
| Rarely | Sometimes | Not stated | Usually | Sometimes | Not stated | 1 Each – Always/rarely/ usually | |
| G34R/V glioma – recurrent | 13 (30.2%) | 8 (18.6%) | 14 (32.6%) | 2 (4.7%) | 1 (2.3%) | 9 (20.9%) | 23 (53.5%) |
| Sometimes | Sometimes | Sometimes | Sometimes | Usually | Sometimes/ Usually | Sometimes/Usually |
The number of respondents selecting each regimen and the most common frequency selected (rarely, sometimes, usually) are shown.
Discussion
To our best knowledge, this study is the first in the literature to describe patterns of care in both diagnosis and treatment of adult HMGs. This survey provides a current snapshot of how histone mutation information is being incorporated into clinical practice. The results were limited by inherent selection biases in how the survey was circulated and who chose to respond. The moderate number of different responding centers, while reasonable it is not large and will also limit interpretation. Significant diversity exists across different countries in regard to the availability of molecular testing and access to clinical trials. Given that one group surveyed was the Caris Precision Oncology Alliance (which provides molecular sequencing services in the USA), providers who have access to molecular sequencing are likely overrepresented in our survey. However, more than half of US responders were from targeted email rather than from the POA, and only 19% of responders overall were from the POA group. Additionally, the survey may have attracted clinicians who are more familiar with HMGs. The retrospective nature of this study also predisposes to an inherent risk of recall bias. This study primarily recruited participants from Australia and the USA, limiting the perspective of clinicians practicing in other locations. For example methylation profiling is not widely used in Australia (due to funding and access restrictions) when compared to other countries.
A smaller number of centers were dual pediatric and adult oncology centers. It is possible that patient management described here may pertain to pediatric patients that have continue under pediatric care beyond 18 years of age. However most questions are focused on initial diagnosis and treatment and so would likely capture only patients diagnosed after 18 years of age. Furthermore given the lower number of associated dual adult-pediatric centers it is unlikely to impact relevance of results.
Despite these limitations, our survey provides useful insight into the current clinical reality of adult HMGs. Approximately 1/3 of respondents included testing for HMG as part of their standard glioma diagnostic workup, while 42% tested if the tumor was located in the midline. Additional indications for testing included younger age and IDH-wildtype histology. The great majority (72%) of those who did not include HMG testing as part of their standard glioma diagnostic workup used a combination of anatomic location and at least one other factor (age or histopathologic features) as their indication for HMG testing. These results suggest that providers pursue HMG testing when demographic, anatomic, and molecular features are atypical for other grade 4 gliomas.
In terms of detection rates, they are likely higher in published cohorts than in the clinical setting. The current diagnostic reality, based on our survey, is that not all H3-mutant gliomas are being detected – not all responders test for HMGs (26% did not test) and not all responders used molecular sequencing (47% only tested with IHC) based on our data. This is in contrast to published cohorts which largely use next generation sequencing or methylation analysis for H3-mutant glioma detection. Furthermore, given the low response rate and likely over representation of molecular testing for DMGs, this may suggest that overall testing rates (including molecular and IHC testing) are even lower in the nonresponders. This bares issues in current and future management of DMGs. For example it could limit referral to centers with expertise, limit data collection and translational research, and slow recruitment for potential future trials.
Almost all participants opted for radiation therapy with concurrent and adjuvant temozolomide (ie the Stupp et al protocol22) as initial treatment for all HMGs (midline K27M, nonmidline K27M, and G34 HMGs). Without any alternative treatment regimen, the Stupp et al protocol currently serves as the de facto treatment standard. The results of our survey mirror recent reports, which show a majority of patients being treated with concurrent temozolomide-radiotherapy and adjuvant temozolomide and a move toward trials in the recurrent setting if available.13,23–25 This differs from the pediatric DMG situation, where radiotherapy alone is the standard treatment due to strong evidence for the ineffectiveness of chemotherapy. In the absence of evidence and guidelines for adult HMG patients, it seems that most clinicians revert to combination concurrent temozolomide/radiotherapy with adjuvant temozolomide as their standard of care for these adult patients despite significant differences in the underlying biology of primary GBM and HMG. Only 19% (n = 8) of respondents enrolled HMG patients in clinical trials as first line treatment.
Given their rarity and lack of effective treatment options, there is a critical need for the coordinated development of molecular testing and clinical trials to evaluate the efficacy and establish practices at the global level. Therefore, the data presented here can stimulate further research in this area including the incorporation of real-world data to further develop a framework for future clinical practice guidelines.
Funding
No funding support was used for this research.
Acknowledgments
We wish to acknowledge the Cooperative Trials Group for Neuro-Oncology (COGNO) and CARIS Precision Oncology Alliance (POA) for assisting in survey distribution.
Conflict of interest statement. No authors have conflict of interest to declare
Authorship statement. Ethics approval contributed by MDS, AY. Writing and distribution of survey contributed to by JTL, KMW, MAK, EL, AY, LS, JS, AL, MK. Data collation contributed by EL and AY. Manuscript was written by AY. All authors have reviewed and approved final manuscript
Group Authorship
The following are participants in the survey who have given permission to acknowledgment of their contribution as group authors (appearing in alphabetical order by last name):
Hamish Alexander, Amir Azadi, Stephen Bagley, Daniel Brungs, Lawrence Cher, Frances Chow, Katharine Cuff, Antonio Di Ieva, Ekokobe Fonkem, Harry Gasper, Craig Gedye, Rebecca Harrison, Melissa James, Dasantha Jayamanne, Wesley M Jose, Santosh Kesari, Lai-Fung Li, Emil Lou, Rimas V Lukas, James Lynam, Angela Mweempwa, Seema Nagpal, Edward Pan, Claire Phillips, Mark Pinkham, Ganes Pranavan, Surabhi Ranjan, Renato V. La Rocca, Daniel Roos, Soma Sengupta, Akanksha Sharma, Hao-Wen Sim, Charlie Teo, Subotheni Thavaneswaran, Yoshie Umemura, Jim Whittle, Joanne Xiu.
