Genetic alterations associated with malignant transformation of sporadic vestibular schwannoma

Incidence of rare malignant transformation in vestibular schwannomas treated with stereotactic radiosurgery: a single-institution analysis of 1,061 cases

PURPOSE

This study assesses the incidence of malignant transformation (MT) in vestibular schwannomas (VSs) treated with stereotactic radiosurgery (SRS) over a 30-year period, with a median follow-up of 12 years.

METHODS

A retrospective analysis was performed on 1,051 individuals who underwent gamma knife surgery (GKS) for VS between May 1991 and March 2023. The cohort comprised 1,013 individuals with sporadic VSs and 38 with neurofibromatosis type 2-related schwannomatosis (NF2-SWN), totaling 1,061 treated VSs. The annual MT risk was calculated based on lesion-years at risk.

RESULTS

Among the 1,061 VSs treated with GKS, MT occurred in 2 cases (0.19%), both in individuals with sporadic VSs. Over 12,940 lesion-years from GKS to the latest follow-up, the annual MT risk was 0.016% for all VSs, with no cases observed within the first 5 years post-GKS. However, the risk increased to 0.025% beyond 5 years. No instances of MT were identified in individuals with NF2-SWN.

CONCLUSIONS

This study represents the most extensive investigation specifically examining the incidence of MT in VSs treated with SRS, leveraging the largest case series and longest observation period to date. The findings indicate that MT following SRS for VSs is exceedingly rare. Although the overall risk remains minimal, it may increase slightly with extended follow-up. These results support the continued use of SRS as a safe and effective treatment for VS while emphasizing the need for long-term monitoring.

Availability and utilization of molecular testing for primary central nervous system tumors among US hospitals

Advanced molecular testing has increasingly become an integral component for accurate diagnosis of central nervous system (CNS) tumors. We sought to establish the current state of molecular testing availability and approaches for the diagnosis of CNS tumors in US hospitals that conduct high volumes of CNS tumor resections. We distributed a 16-item survey inquiring about molecular testing approaches for CNS tumors to 115 neuropathologists at US hospitals with neurosurgery residency programs. Thirty-five neuropathologists (30.4%) responded to the survey, all of whom indicated their institutions perform molecular testing on CNS tumor tissue. The most commonly offered tests were MGMT methylation profiling and next-generation sequencing. Fourteen respondents (40%) indicated that their institution is able to test for and report all of the molecular alterations included in our survey. Nine (25.7%) respondents indicated that molecular testing is performed as standard of care for all patients with resected CNS tumors. Our results suggest that even in academic hospitals with a high volume of CNS tumor resections, molecular testing for these tumors is limited. Continued initiatives are necessary to expand the availability of molecular testing for CNS tumors to ensure diagnostic accuracy and guide targeted therapy.

Malignant melanotic nerve sheath tumor with PRKAR1A, KMT2C, and GNAQ mutations

Malignant melanotic nerve sheath tumor (MMNST) is a rare and potentially aggressive lesion defined in the 2021 WHO Classification of Tumors of the Central Nervous System. MMNST demonstrate overlapping histologic and clinical features of schwannoma and melanoma. MMNST often harbor PRKAR1A mutations, especially within the Carney Complex. We present a case of aggressive MMNST of the sacral region in a 48-year-old woman. The tumor contained PRKAR1A frameshift pR352Hfs*89, KMT2C splice site c.7443-1G>T and GNAQ p.R183L missense mutations, as well as BRAF and MYC gains. Genomic DNA methylation analysis using the Illumina 850K EpicBead chip revealed that the lesion did not match an established methylation class; however, uniform manifold approximation and projection (UMAP) placed the tumor very near schwannomas. The tumor expressed PD-L1, and the patient was treated with radiation and immune checkpoint inhibitors following en bloc resection. Although she had symptomatic improvement, she suffered early disease progression with local recurrence, and distant metastases, and died 18 months after resection. It has been suggested that the presence of GNAQ mutations can differentiate leptomeningeal melanocytic neoplasms and uveal melanoma from MMNST. This case and others demonstrate that GNAQ mutations may exist in malignant nerve sheath tumors; that GNAQ and PRKAR1A mutations are not always mutually exclusive and that neither can be used to differentiate MMNST or MPNST from all melanocytic lesions.