Translational significance of CDKN2A/B homozygous deletion in isocitrate dehydrogenase-mutant astrocytoma

Isocitrate dehydrogenase (IDH) 1 or 2 mutations confer a favorable prognosis compared to IDH-wildtype in astrocytoma, frequently denoting a lower grade malignancy. However, recent molecular profiling has identified specific aggressive tumor subgroups with clear clinical prognostic implications that are independent of histologic grading. The homozygous deletion of CDKN2A/B is the strongest implicated independent indicator of the poor prognosis within IDH-mutant astrocytoma, and the identification of this alteration in these lower histologic grade tumors transforms their biology toward an aggressive grade 4 phenotype clinically. CDKN2A/B homozygous deletion is now sufficient to define a grade 4 tumor in IDH-mutant astrocytomas regardless of histologic appearance, yet there are currently no effective molecularly informed targeted therapies for these tumors. The biological impact of CDKN2A/B homozygous deletion in IDH-mutant tumors and the optimal treatment strategy for this molecular subgroup remains insufficiently explored. Here we review the current understanding of the translational significance of homozygous deletion of CDKN2A/B gene expression in IDH-mutant astrocytoma and associated diagnostic and therapeutic implications.

Role of CDKN2A deletion in grade 2/3 IDH-mutant astrocytomas: need for selective approach in resource-constrained settings

OBJECTIVE

The authors aimed to assess the frequency of homozygous CDKN2A deletion in isocitrate dehydrogenase (IDH)-mutant diffuse astrocytomas (grade 2/3) and to narrow down the clinicopathological indications in which the CDKN2A fluorescence in situ hybridization (FISH) assay is cost-effective in resource-constrained settings.

METHODS

IDH-mutant astrocytomas were analyzed for ATRX, p53, MIB1-LI, and p16 expression using immunohistochemistry. The FISH assay was used to evaluate CDKN2A deletion and 1p/19q codeletion. Survival outcomes were assessed according to the different molecular markers.

RESULTS

A total of 150 adult patients with IDH-mutant grade 2 (n = 95) and grade 3 (n = 55) astrocytomas (145 primary and 5 recurrent) were analyzed. Using a cutoff value of 30% for defining significant homozygous CDKN2A deletion, none of the grade 2 and 10.9% (6/55) of grade 3 astrocytomas showed this deletion (4 primary and 2 recurrent grade 3 tumors) and were reclassified as grade 4. This mutation was more frequent in recurrent (40%, 2/5) than primary (2.76%, 4/145) gliomas. Half (3/6, 50%) of the CDKN2A-deleted cases demonstrated poor outcomes; 2 of these cases experienced recurrence at 12 and 36 months after surgery, and 1 died at 5 months. The majority of CDKN2A-deleted cases showed marked cellularity (100%), pleomorphism (100%), brisk mitosis (83.3%), and tumor giant cell formation (83.4%). None of the cases with retained p16 expression harbored this deletion. Both overall survival (p = 0.039) and progression-free survival (p = 0.0045) were found to be worse in cases with p16 loss. Selectively performing CDKN2A FISH only in high-risk cases with histomorphological features of anaplasia, p16 loss, or recurrent tumors achieved a sensitivity and negative predictive value of 100%. This approach would have resulted in saving 41.1% of the original expenditure ($6900 US per 150 samples) and 27.6 person-minutes per sample without compromising the identification of deleted cases.

CONCLUSIONS

Homozygous CDKN2A deletion is conspicuously absent in grade 2 and rare in primary grade 3 IDH-mutant astrocytomas. The authors propose that restricting use of the FISH assay to cases showing histomorphological features of anaplasia, p16 loss, or recurrent tumors will help this platform to be utilized in the most cost-effective manner in resource-constrained settings.

Case report: Pseudoprogression mimicking neoplastic recurrence three months after completion of proton beam therapy for an IDH-mutant astrocytoma CNS WHO grade 3

Background

Radiation-induced changes following proton beam therapy in isocitrate dehydrogenase (IDH)-mutated diffuse central nervous system (CNS) World Health Organization (WHO) grade 2 and 3 gliomas are not well characterized. We present a patient with an IDH-mutant astrocytoma CNS WHO grade 3 treated with proton beam therapy and with postradiation MRI changes suggestive of neoplastic progression that surprisingly turned out to be reactive.

Case presentation

A man in his twenties underwent surgery with a near gross total resection for what turned out to be an IDH-mutant astrocytoma CNS WHO grade 3. He was included in the PRO-GLIO trial and randomized to receive proton beam therapy to a total dose of 59.4 Gray (Gy) relative biological effectiveness (RBE). Four weeks after completion of radiotherapy, adjuvant temozolomide was commenced. All treatment was well tolerated, and the patient was in excellent general condition. Surprisingly, magnetic resonance imaging (MRI) examination three months after completion of radiotherapy showed what was highly suggestive of a distant recurrence. The patient underwent resective surgery about seven months after his first surgery. Histological examination showed inflammatory changes without neoplastic tissue, albeit not very typical for postradiation changes. Adjuvant chemotherapy with temozolomide was continued.

Conclusion

The presented case clearly shows that caution must be taken when interpreting cerebral MRI changes postradiation, and in particular after proton therapy. Further understanding of this subject is crucial to distinguish between patients requiring intensified antineoplastic treatment and those for whom maintaining current therapy or ongoing watchful waiting is advisable.

Prognostic Impact of TERT Promoter Mutations in Adult-Type Diffuse Gliomas Based on WHO2021 Criteria

Mutation in the telomerase reverse transcriptase promoter (TERTp )is commonly observed in various malignancies, such as central nervous system (CNS) tumors, malignant melanoma, bladder cancer, and thyroid carcinoma. These mutations are recognized as significant poor prognostic factors for these tumors. In this investigation, a total of 528 cases of adult-type diffuse gliomas diagnosed at a single institution were reclassified according to the 2021 WHO classifications of CNS tumors, 5th edition (WHO2021). The study analyzed clinicopathological and genetic features, including TERTp mutations in each tumor. The impact of known prognostic factors on patient outcomes was analyzed through Kaplan-Meier survival and Cox regression analysis. TERTp mutations were predominantly identified in 94.1% of oligodendrogliomas (ODG), followed by 66.3% in glioblastoma, IDH-wildtype (GBM-IDHwt), and 9.2% of astrocytomas, IDH-mutant (A-IDHm). When considering A-IDHm and GBM as astrocytic tumors (Group 1) and ODGs (Group 2), TERTp mutations emerged as a significant adverse prognostic factor (p = 0.013) in Group 1. However, within each GBM-IDHwt and A-IDHm, the presence of TERTp mutations did not significantly impact patient prognosis (p = 0.215 and 0.268, respectively). Due to the high frequency of TERTp mutations in Group 2 (ODG) and their consistent prolonged survival, a statistical analysis to evaluate their impact on overall survival was deemed impractical. When considering MGMTp status, the combined TERTp-mutated and MGMTp-unmethylated group exhibited the worst prognosis in OS (p = 0.018) and PFS (p = 0.034) of GBM. This study confirmed that the classification of tumors according to the WHO2021 criteria effectively reflected prognosis. Both uni- and multivariate analyses in GBM, age, MGMTp methylation, and CDKN2A/B homozygous deletion were statistically significant prognostic factors while in univariate analysis in A-IDHm, grade 4, the Ki-67 index and MYCN amplifications were statistically significant prognostic factors. This study suggests that it is important to classify and manage tumors based on their genetic characteristics in adult-type diffuse gliomas.

Epidemiological analysis of adult-type diffuse lower-grade gliomas and incidence and prevalence estimates of diffuse IDH-mutant gliomas in France

BACKGROUND

The recent advent of anti-IDH therapies and changes in the WHO classification of gliomas implies estimating the number of patients who could benefit (or not) from anti-IDH treatment. As published data on the current incidence of different subtypes of IDH-mutant gliomas (based on the latest histomolecular WHO classification) are lacking in many countries. The present analysis aims to review the main factors impacting the incidence of gliomas and lower-grade gliomas and to estimate the incidence and prevalence of IDH-mutant gliomas in France.

METHODS

Our analysis was based on data from the French Brain Tumor DataBase and literature.

RESULTS

Case definition, recording methods, histological classifications, age, sex, ethnicity, ancestry, environment, genetics, etc., impact the incidence of gliomas overall and lower-grade gliomas. In France, for the year 2024, the incidence estimates of all gliomas and all adult-type diffuse IDH-mutant gliomas are 6.6/100,000 and 1/100,000 person-years, respectively. The incidence estimates of grades 2, 3, and 4 diffuse IDH-mutant gliomas are 0.5, 0.3, 0.2 per 100,000 person-years, respectively. Of note, the incidence estimate of grade 3 diffuse IDH-mutant glioma versus grade 2 or 4 is slightly more difficult to assess due to the possible variability in histological criteria to define tumor grade. The prevalence of diffuse IDH-mutant grade 2 glioma would be more than 6.57/100,000 persons.

DISCUSSION/CONCLUSION

Our epidemiological analysis provides estimates of potential number of patients, but large prospective real-world studies are required to determine the positioning of anti-IDH treatments among all therapeutic strategies [surgery(ies), chemotherapy(ies), radiotherapy(ies), clinical/radiological follow-up, etc.].

CLINICAL utility of assessing CDKN2A status in recurrent astrocytomas

IDH-mutant astrocytomas exhibit a more indolent natural history and better prognosis compared to their IDH-wild type counterparts. WHO 2021 classification integrated CDKN2A/B homozygous deletion as a crucial criterion for grading these tumors, emphasizing its prognostic implications. FISH assay is commonly used to assess CDKN2A status, but guidelines for interpreting FISH results for glioma prognostication are not well-defined in the literature. We conducted an ambispective study involving 22 cases of recurrent IDH-mutant astrocytomas, including primary tumor samples. Histopathological assessments, including WHO grading and molecular profiling, were performed. Immunohistochemistry confirmed IDH mutation status, and FISH analysis evaluated CDKN2A homozygous deletion. Homozygous CDKN2A deletion was detected in only 1/22 (4.8%) of primary tumors, which was grade 3 astrocytoma, and significantly more frequent in recurrent cases, particularly in histological grade 2/3 tumors (35.3%). Patients harboring CDKN2A deletions exhibited significantly poorer overall survival, highlighting its prognostic significance. Our findings highlight the clinical relevance of CDKN2A assessment in recurrent IDH-mutant astrocytomas and its utility as a prognostic marker. We propose a selective approach to FISH testing, focusing on primary grade 3 and all recurrent cases, regardless of histology grade, to optimize diagnostic accuracy and stratification for personalized treatment strategies.

Spontaneous Shrinkage of isocitrate dehydrogenase (IDH)-mutant astrocytoma caused by intra-tumoural cyst rupture: a case report

BACKGROUND

T2-fluid-attenuated inversion recovery (FLAIR) mismatch sign is a specific imaging finding of isocitrate dehydrogenase (IDH)-mutant astrocytomas. Histologically, a hypointense area on FLAIR images indicates the presence of microcysts. Here we report a case of IDH-mutant astrocytoma that shrunk spontaneously.

CASE DESCRIPTION

A 26-year-old woman presented with a complaint of headache. Her magnetic resonance (MR) images revealed a lesion mass with a T2-FLAIR mismatch sign in the left frontal lobe. Subsequently, after 1 month, she was referred to our department, and we found that the lesion had unexpectedly shrunk; however, no further shrinkage was observed in the next 3 months. Furthermore, a biopsy was performed, and the results indicated a diagnosis of astrocytoma, IDH-mutant CNS WHO grade 3. Thus, she underwent subtotal resection. We found no neurological deficits in the patient, and she received 60 Gy of radiotherapy at the local site and chemotherapy with nimustine hydrochloride (ACNU), followed by the administration of ACNU every 8 weeks for 2 years. Overall, after 36 months of tumour resection, she was in good health and exhibited no recurrence. Notably, her histological and MR image findings suggested that the macroscopic cyst was formed by the fusion of microcysts, which is a characteristic feature of IDH-mutant astrocytoma with a T2-FLAIR mismatch sign, and that the tumour shrunk because of the rupture of the cyst in the Sylvian cistern.

CONCLUSION

The present case report suggests that IDH-mutant astrocytoma cannot be ruled out even when the lesion shrinks spontaneously.

Enhancing glioma care with advanced imaging: T2-FLAIR mismatch as a predictive biomarker in IDH-mutant astrocytoma

The study highlights that diffuse glioma, a prevalent type of brain tumor, affect approximately 100,000 individuals worldwide each year. IDH-mutant astrocytoma and oligodendrogliomas typically have a more favorable prognosis compared to IDH-wildtype glioblastomas. However, many IDH-mutant astrocytoma has the potential to progress to grade 4 glioblastomas, leading to a less favorable prognosis. In a recent investigation, Shumpei Onishi et al. examined the T2-FLAIR mismatch sign as a possible imaging biomarker for assessing CDKN2A status in non-enhancing IDH-mutant astrocytoma. The findings indicate that the T2-FLAIR mismatch sign is linked to CDKN2A-intact astrocytoma, providing a valuable tool for diagnostic and prognostic purposes. Additionally, the use of Indocyanine Green (ICG) for real-time visualization during neurosurgical procedures demonstrates potential, though it may have limitations in specificity. While these advancements offer promise in glioma management, there remains a critical need for larger, standardized studies to validate these findings and further improve treatment outcomes.