Therapy for Diffuse Astrocytic and Oligodendroglial Tumors in Adults: ASCO-SNO Guideline

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD₂) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower D_max and D_1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D_99% and D_min were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D_20%, D_40%, D_60% and D_80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the D_max in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

Key Clinical Principles in the Management of Glioblastoma

Glioblastoma is the most common and aggressive primary brain tumor in the adult population and leads to considerable morbidity and mortality. It has a dismal prognosis with average survival of 15-18 months, and the current standard-of-care treatment paradigm includes maximal surgical resection and postoperative concurrent chemoradiotherapy and maintenance chemotherapy, with consideration of Tumor Treating Fields. There is a major emphasis to enroll patients onto ongoing clinical trials to further improve treatment outcomes, given the aggressive nature of the disease course and poor patient survival. Recent research efforts have focused on radiotherapy dose intensification, regulation of the tumor microenvironment, and exploration of immunotherapeutic approaches to overcome the barriers to treatment. This review article outlines the current evidence-based management principles as well as reviews recent clinical trial data and ongoing clinical studies evaluating novel therapeutic options.

Proton radiotherapy in the treatment of IDH-mutant diffuse gliomas: an early experience from shanghai proton and heavy ion center

PURPOSE

According to the presence or absence of isocitrate dehydrogenase (IDH) mutation, the 2021 WHO classification system bisected diffuse gliomas into IDH-mutant tumors and IDH-wildtype tumors. This study was aimed to evaluate the outcomes of proton radiotherapy treating IDH-mutant diffuse gliomas.

PATIENTS AND METHODS

Between May 2015 and May 2022, a total of 52 consecutive patients with IDH-mutant diffuse gliomas were treated at Shanghai Proton and Heavy Ion Center. Tumor histologies were 33 cases of astrocytoma and 19 cases of oligodendroglioma. Tumor classified by WHO grade 2, 3 and 4 were 22, 25, and 5 cases, respectively. All 22 patients with WHO grade 2 tumors and one patient with brain stem WHO grade 4 tumor were irradiated with 54GyE. The other 29 patients with WHO grade 3 and 4 tumors were irradiated with 60GyE. Temozolomide was recommended to all patients, and was eventually conducted in 50 patients.

RESULTS

The median follow-up time was 21.7 months. The 12/24-month progression-free survival (PFS) and overall survival (OS) rates for the entire cohort were 97.6%/78.4% and 100%/91.0% group. Examined by both univariate and multivariate analysis, WHO grade of tumor were of the most significant impact for both PFS and OS. No severe acute toxicity (grade 3 or above) was found. In terms of late toxicity, grade 3 radio-necrosis was developed in one case of oligodendroglioma, WHO grade 3.

CONCLUSION

Proton radiotherapy produced a favorable outcome with acceptable adverse-effects in patients with IDH-mutant diffuse gliomas.

Cell-Population Dynamics in Diffuse Gliomas during Gliomagenesis and Its Impact on Patient Survival

Diffuse gliomas continue to be an important problem in neuro-oncology. To solve it, studies have considered the issues of molecular pathogenesis from the intratumoral heterogeneity point. Here, we carried out a comparative dynamic analysis of the different cell populations' content in diffuse gliomas of different molecular profiles and grades, considering the cell populations' functional properties and the relationship with patient survival, using flow cytometry, immunofluorescence, multiparametric fluorescent in situ hybridization, polymerase chain reaction, and cultural methods. It was shown that an increase in the IDH-mutant astrocytomas and oligodendrogliomas malignancy is accompanied by an increase in stem cells' proportion and mesenchymal cell populations' appearance arising from oligodendrocyte-progenitor-like cells with cell plasticity and cells' hypoxia response programs' activation. In glioblastomas, malignancy increase is accompanied by an increase in both stem and definitive cells with mesenchymal differentiation, while proneuronal glioma stem cells are the most likely the source of mesenchymal glioma stem cells, which, in hypoxic conditions, further give rise to mesenchymal-like cells. Clinical confirmation was a mesenchymal-like cell and mesenchymal glioma stem cell number, and the hypoxic and plastic molecular programs' activation degree had a significant effect on relapse-free and overall survival. In general, we built a multi-vector model of diffuse gliomas' pathogenetic tracing up to the practical plane.

Conventional and emerging treatments of astrocytomas and oligodendrogliomas

PURPOSE

Astrocytomas and oligodendrogliomas are mainly diffuse primary brain tumors harboring a diagnostic and prognostically favorable isocitrate dehydrogenase mutation. They are still incurable besides growing molecular knowledge and therapy options. Circumscribed astrocytomas are also discussed here, although they represent a separate entity despite similarities in the nomenclature.

METHODS

We reviewed clinical trials, preclinical approaches as well as guideline recommendations form the major scientific Neuro-Oncology organizations for astrocytomas and oligodendrogliomas according to PRISMA guidelines.

RESULTS

After histopathological diagnosis and eventually a maximal safe resection, patients with good prognostic factors may be followed by magnetic resonance imaging (MRI). If further treatment is necessary, either after diagnosis or at progression, diffuse astrocytomas and oligodendrogliomas are mainly treated with combined radiochemotherapy or maximal safe resection followed by combined radiochemotherapy according to current guidelines based on randomized trials. Circumscribed gliomas like pilocytic astrocytomas, CNS WHO grade 1, or pleomorphic xanthoastrocytomas, CNS WHO grade 2, are often treated with surgery alone. Current approaches for therapy optimization include decision of the best chemotherapy regimen. The IDH mutation presents a rational target for small molecule inhibition and immune therapy in diffuse astrocytomas and oligodendrogliomas, while the BRAF pathway is frequently mutated and treatable in circumscribed gliomas.

CONCLUSION

Despite establishment of standard treatment approaches for gliomas that include resection, radio- and chemotherapy, there is a lack of effective treatments for progressive disease. Immune- and targeted therapies are currently investigated.

World Health Organization 2021 Classification of Central Nervous System Tumors and Implications for Therapy for Adult-Type Gliomas: A Review

Importance

Previous histologic classifications of brain tumors have been limited by discrepancies in diagnoses reported by neuropathologists and variability in outcomes and response to therapies. Such diagnostic discrepancies have impaired clinicians' ability to select the most appropriate therapies for patients and have allowed heterogeneous populations of patients to be enrolled in clinical trials, hindering the development of more effective therapies. In adult-type diffuse gliomas, histologic classification has a particularly important effect on clinical care.

Observations

In 2021, the World Health Organization published the fifth edition of the Classification of Tumors of the Central Nervous System. This classification incorporates advances in understanding the molecular pathogenesis of brain tumors with histopathology in order to group tumors into more biologically and molecularly defined entities. As such, tumor classification is significantly improved through better characterized natural histories. These changes have particularly important implications for gliomas. For the first time, adult- and pediatric-type gliomas are classified separately on the basis of differences in molecular pathogenesis and prognosis. Furthermore, the previous broad category of adult-type diffuse gliomas has been consolidated into 3 types: astrocytoma, isocitrate dehydrogenase (IDH) mutant; oligodendroglioma, IDH mutant and 1p/19q codeleted; and glioblastoma, IDH wild type. These major changes are driven by IDH mutation status and include the restriction of the diagnosis of glioblastoma to tumors that are IDH wild type; the reclassification of tumors previously diagnosed as IDH-mutated glioblastomas as astrocytomas IDH mutated, grade 4; and the requirement for the presence of IDH mutations to classify tumors as astrocytomas or oligodendrogliomas.

Conclusions and Relevance

The 2021 World Health Organization central nervous system tumor classification is a major advance toward improving the diagnosis of brain tumors. It will provide clinicians with more accurate guidance on prognosis and optimal therapy for patients and ensure that more homogenous patient populations are enrolled in clinical trials, potentially facilitating the development of more effective therapies.

Molecular testing for adolescent and young adult central nervous system tumors: A Canadian guideline

The 2021 World Health Organization (WHO) classification of CNS tumors incorporates molecular signatures with histology and has highlighted differences across pediatric vs adult-type CNS tumors. However, adolescent and young adults (AYA; aged 15–39), can suffer from tumors across this spectrum and is a recognized orphan population that requires multidisciplinary, specialized care, and often through a transition phase. To advocate for a uniform testing strategy in AYAs, pediatric and adult specialists from neuro-oncology, radiation oncology, neuropathology, and neurosurgery helped develop this review and testing framework through the Canadian AYA Neuro-Oncology Consortium. We propose a comprehensive approach to molecular testing in this unique population, based on the recent tumor classification and within the clinical framework of the provincial health care systems in Canada.

Current and Future Frontiers of Molecularly Defined Oligodendrogliomas

Oligodendrogliomas are a subtype of adult diffuse glioma characterized by their better responsiveness to systemic chemotherapy than other high-grade glial tumors. The World Health Organization (WHO) 2021 brain tumor classification highlighted defining molecular markers, including 1p19q codeletion and IDH mutations which have become key in diagnosing and treating oligodendrogliomas. The management for patients with oligodendrogliomas includes observation or surgical resection potentially followed by radiation and chemotherapy with PCV (Procarbazine, Lomustine, and Vincristine) or Temozolomide. However, most of the available research about oligodendrogliomas includes a mix of histologically and molecularly diagnosed tumors. Even data driving our current management guidelines are based on post-hoc subgroup analyses of the 1p19q codeleted population in landmark prospective trials. Therefore, the optimal treatment paradigm for molecularly defined oligodendrogliomas is incompletely understood. Many questions remain open, such as the optimal timing of radiation and chemotherapy, the response to different chemotherapeutic agents, or what genetic factors influence responsiveness to these agents. Ultimately, oligodendrogliomas are still incurable and new therapies, such as targeting IDH mutations, are necessary. In this opinion piece, we present relevant literature in the field, discuss current challenges, and propose some studies that we think are necessary to answer these critical questions.

Tumor-Associated Microenvironment of Adult Gliomas: A Review

The glioma-associated tumor microenvironment involves a multitude of different cells ranging from immune cells to endothelial, glial, and neuronal cells surrounding the primary tumor. The interactions between these cells and glioblastoma (GBM) have been deeply investigated while very little data are available on patients with lower-grade gliomas. In these tumors, it has been demonstrated that the composition of the microenvironment differs according to the isocitrate dehydrogenase status (mutated/wild type), the presence/absence of codeletion, and the expression of specific alterations including H3K27 and/or other gene mutations. In addition, mechanisms by which the tumor microenvironment sustains the growth and proliferation of glioma cells are still partially unknown. Nonetheless, a better knowledge of the tumor-associated microenvironment can be a key issue in the optic of novel therapeutic drug development.

Comparative efficacy and safety of therapeutics for elderly glioblastoma patients: A Bayesian network analysis

Optimal management strategies for elderly glioblastoma (GBM) patients remain elusive. Overall survival (OS) and progression-free survival (PFS) in elderly newly diagnosed GBM (ndGBM) patients were analyzed with random-effects Bayesian network meta-analysis with the estimated hazard ratio (HR) with a 95% confidence interval (95% CrI). In addition, OS, PFS and adverse event (AE) data on ndGBM and recurrent GBM (rGBM) were assessed. Seventeen eligible trials with 12 on ndGBM and 5 on rGBM were identified. For the improvements it induced in the OS of elderly ndGBM patients, tumor treating field (TTF) + temozolomide (TMZ) (HR: 0.11, 95% CrI: 0.02-0.67 vs. supportive care (SPC)) ranked first, followed by TMZ + hyperfractionated radiotherapy (HFRT) (HR: 0.17, 95% CrI: 0.03-0.95 vs. SPC). For the improvements it induced in the PFS of elderly ndGBM patients, bevacizumab (BEV) + HFRT ranked first, followed by TMZ + HFRT. TMZ was observed to be more effective in O6-methylguanine-DNA-methyltransferase (MGMT) promoter-methylated ndGBM patients than HFRT and standard radiotherapy (STRT). For elderly rGBM patients, the treatments included were comparable. The rates of other neurological symptoms (16.1%) and lymphocytopenia (10.4%) were higher in ndGBM patients; lymphocytopenia (10.3%) and infection (8.1%) were higher in rGBM patients among the ≥ 3 grade AEs. TMZ-related AEs should be further considered. In conclusion, TTF + adjuvant TMZ and TMZ + HFRT are most likely to be recommended for elderly ndGBM patients. No best treatment for rGBM in elderly patients is illustrated. TMZ is identified to be more effective in elderly ndGBM patients with methylated MGMT status; however, AEs associated with TMZ-related therapy should be well considered and managed.

The Overview of Practical Guidelines for Gliomas by KSNO, NCCN, and EANO

Gliomas have been histologically diagnosed as the third most common primary tumor of the central nervous system (CNS) in a relatively small portion of Korea. Despite the rarity of gliomas, the disease entity is very dynamic due to its various molecular characteristics, compared with other CNS tumors. The practice of managing glioma patients is not globally established as a precise standard guideline because of the different socio-medical environments of individual countries. The Korean Society for Neuro-Oncology (KSNO) published guidelines for managing adult glioma in 2019, and the National Comprehensive Cancer Network and European Association of Neuro-Oncology published guidelines in September 2021 and March 2021, respectively. However, these guidelines have several different recommendations in practice, including tissue management, adjuvant treatment after surgical resection, and salvage treatment for recurrent/progressive gliomas. Currently, the KSNO guideline working group is preparing an updated version of the guideline for managing adult gliomas. In this review, common features have been verified and different points are analyzed. Consequently, this review is expected to be informative and helpful to provide high quality evidence and a strong recommendation level for the establishment of new KSNO guidelines for managing gliomas.