Long-term growth rate of vestibular schwannoma in neurofibromatosis 2: A volumetric consideration

Brigatinib in NF2-Related Schwannomatosis with Progressive Tumors

BACKGROUND

NF2-related schwannomatosis (NF2-SWN, formerly called neurofibromatosis type 2) is a tumor predisposition syndrome that is manifested by multiple vestibular schwannomas, nonvestibular schwannomas, meningiomas, and ependymomas. The condition is relentlessly progressive with no approved therapies. On the basis of preclinical activity of brigatinib (an inhibitor of multiple tyrosine kinases) in NF2-driven nonvestibular schwannoma and meningioma, data were needed on the use of brigatinib in patients with multiple types of progressive NF2-SWN tumors.

METHODS

In this phase 2 platform trial with a basket design, patients who were 12 years of age or older with NF2-SWN and progressive tumors were treated with oral brigatinib at a dose of 180 mg daily. A central review committee evaluated one target tumor and up to five nontarget tumors in each patient. The primary outcome was radiographic response in target tumors. Key secondary outcomes were safety, response rate in all tumors, hearing response, and patient-reported outcomes.

RESULTS

A total of 40 patients (median age, 26 years) with progressive target tumors (10 vestibular schwannomas, 8 nonvestibular schwannomas, 20 meningiomas, and 2 ependymomas) received treatment with brigatinib. After a median follow-up of 10.4 months, the percentage of tumors with a radiographic response was 10% (95% confidence interval [CI], 3 to 24) for target tumors and 23% (95% CI, 16 to 30) for all tumors; meningiomas and nonvestibular schwannomas had the greatest benefit. Annualized growth rates decreased for all tumor types during treatment. Hearing improvement occurred in 35% (95% CI, 20 to 53) of eligible ears. Exploratory analyses suggested a decrease in self-reported pain severity during treatment (-0.013 units per month; 95% CI, -0.002 to -0.029) on a scale from 0 (no pain) to 3 (severe pain). No grade 4 or 5 treatment-related adverse events were reported.

CONCLUSIONS

Brigatinib treatment resulted in radiographic responses in multiple tumor types and clinical benefit in a heavily pretreated cohort of patients with NF2-SWN. (Funded by the Children's Tumor Foundation and others; INTUITT-NF2 ClinicalTrials.gov number, NCT04374305.).

The genetic landscape and possible therapeutics of neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) is a genetic condition marked by the development of multiple benign tumors in the nervous system. The most common tumors associated with NF2 are bilateral vestibular schwannoma, meningioma, and ependymoma. The clinical manifestations of NF2 depend on the site of involvement. Vestibular schwannoma can present with hearing loss, dizziness, and tinnitus, while spinal tumor leads to debilitating pain, muscle weakness, or paresthesias. Clinical diagnosis of NF2 is based on the Manchester criteria, which have been updated in the last decade. NF2 is caused by loss-of-function mutations in the NF2 gene on chromosome 22, leading the merlin protein to malfunction. Over half of NF2 patients have de novo mutations, and half of this group are mosaic. NF2 can be managed by surgery, stereotactic radiosurgery, monoclonal antibody bevacizumab, and close observation. However, the nature of multiple tumors and the necessity of multiple surgeries over the lifetime, inoperable tumors like meningiomatosis with infiltration of the sinus or in the area of the lower cranial nerves, the complications caused by the operation, the malignancies induced by radiotherapy, and inefficiency of cytotoxic chemotherapy due to the benign nature of NF-related tumors have led a march toward exploring targeted therapies. Recent advances in genetics and molecular biology have allowed identifying and targeting of underlying pathways in the pathogenesis of NF2. In this review, we explain the clinicopathological characteristics of NF2, its genetic and molecular background, and the current knowledge and challenges of implementing genetics to develop efficient therapies.

Natural History of Brachial Plexus, Peripheral Nerve, and Spinal Schwannomas

BACKGROUND

Management of sporadic schwannomas is often dictated by a patient's clinical presentation and the tumor's behavior. For patients who are managed nonsurgically, there are little data available about the expected natural history.

OBJECTIVE

To evaluate the natural history and growth patterns of extracranial schwannomas including tumors of the distal peripheral nerves, spine, and brachial plexus.

METHODS

A retrospective review was performed to identify patients with nonsyndromic extracranial schwannomas at a single tertiary care institution diagnosed between 2002 and 2019. Patient data and tumor characteristics including volume were recorded.

RESULTS

Two hundred twenty-seven patients were identified (mean age 51 years, 42% male, average of 27.8-month follow-up). Tumor location was distal peripheral nerve in 82, brachial plexus in 36, and paraspinal in 109. At the time of diagnosis, peripheral lesions were significantly larger than spinal (59 m 3 vs 13 cm 3 ) and brachial plexus lesions (15 cm 3 ). Distinct growth patterns were seen with both distal peripheral nerve and spinal lesions; 34/82 peripheral nerve lesions had fast growth (β = 0.176%/day), and 48 had slow growth (β = 0.021%/day; P < .01). Spinal schwannomas similarly had 30 fast-growing (β = 0.229%/day), 16 moderate-growing (β = 0.071%/day), and 63 slow-growing (β = 0.022%/day; P = .03) subtypes. The brachial plexus had relatively homogeneous growth patterns (β = 0.065%/day). Females had 2.9 times greater odds of having the fast-growing subtype.

CONCLUSION

Distinct growth patterns were seen in extracranial sporadic schwannomas based on tumor location and patient demographics. Fast (>80% volume change per year) vs slow (5%-10% per year) tumor growth can often be ascertained within 2 follow-up images. Awareness of these patterns might have implications for patient counseling and therapeutic decision-making.

Prevalence and natural history of schwannomas in neurofibromatosis type 2 (NF2): the influence of pathogenic variants

This study explores the natural history of vestibular, trigeminal and lower cranial nerve schwannomas (VS, TS, LCNS) in patients with Neurofibromatosis type 2 (NF2), to understand how pathogenic variants (PVs) of the NF2 gene affect tumour burden and growth rate, via a retrospective analysis of a UK NF2 centre database and imaging. VS, TS and LCNS location and size were measured in accordance with a standardised protocol. PVs were categorised in accordance with the UK NF2 Genetic Severity Score (GSS). 153 patients (age 5-82) had 458 schwannomas, of which 362 were previously untreated comprising: 204 VS, 93 TS, and 65 LCNS (IX, X, XI). 322 schwannomas had sequential imaging allowing growth rate analysis with a mean follow-up of 45 months. VS were universally present, and bilateral in 146/153 cases. 65% of tumours grew >2 mm during the study period at mean rate 2.0 mm/year. Significant association was found between increasing GSS and growth rate. TS occurred in 66/153 patients (bilateral in 27/153); 31% of tumours showed growth (mean 1.8 mm/yr). Significant increase in tumour prevalence was noted with increasing GSS. LCNS were found in 47/153 patients (bilateral in 19/153); 27% of tumours showed growth (mean 1.9 mm/yr). The trend for increased prevalence with increasing GSS did not reach significance. VS growth rate was significantly influenced by GSS and they were much more likely to grow than TS and LCNS. TS prevalence also correlated with increasing GSS.

Comparison of the Signal Intensity of Vestibular Schwannoma Between Growing and Nongrowing Tumors

OBJECTIVES/HYPOTHESIS

To determine the relationship between signal intensity on gadolinium (Gd)-enhanced magnetic resonance images and growth of vestibular schwannomas (VSs).

STUDY DESIGN

Cross-sectional study.

METHODS

In this cross-sectional study, we retrospectively reviewed the data of 31 patients with VSs who underwent magnetic resonance imaging (MRI). The mean signal intensities within the regions of interest in the tumor, pons, and temporal muscles were measured on Gd-enhanced T1-weighted MRI. Relative intensity ratios were calculated as follows: T/N pons ratio (T/Np) is the tumor signal intensity/pons signal intensity and T/N muscle ratio (T/Nm) is the tumor signal intensity/temporal muscle signal intensity. Volume measurements were used to assess the tumor size. Growth rate was determined by assessing previous imaging studies. Growing VS was defined as a tumor with a growth rate >100 mm³ /year.

RESULTS

The mean (standard deviation) T/Np and T/Nm were 1.47 (0.27) and 1.50 (0.24), respectively, in nongrowing tumors and 1.78 (0.17) and 1.90 (0.12), respectively, in growing tumors. The T/Np and T/Nm differed significantly between the two groups (T/Np, P < .001; T/Nm, P < .001). Receiver operating characteristic curve analysis showed that cutoffs of 1.56 and 1.76 for T/Np (93.33% sensitivity, 75.00% specificity) and T/Nm (100.00% sensitivity, 93.75% specificity), respectively, could be used to diagnose a growth rate of >100 mm³ /year. The area under the curve was 0.85 (95% confidence interval, 0.70-1.00) for T/Np and 0.94 (0.82-1.00) for T/Nm.

CONCLUSION

Growing VSs show higher signal intensities on Gd-enhanced MRI. Thus, measuring the signal intensity of VS on Gd-enhanced MRI may aid in predicting VS growth.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Current Understanding of Neurofibromatosis Type 1, 2, and Schwannomatosis

Neurofibromatosis (NF) is a neurocutaneous syndrome characterized by the development of tumors of the central or peripheral nervous system including the brain, spinal cord, organs, skin, and bones. There are three types of NF: NF1 accounting for 96% of all cases, NF2 in 3%, and schwannomatosis (SWN) in <1%. The NF1 gene is located on chromosome 17q11.2, which encodes for a tumor suppressor protein, neurofibromin, that functions as a negative regulator of Ras/MAPK and PI3K/mTOR signaling pathways. The NF2 gene is identified on chromosome 22q12, which encodes for merlin, a tumor suppressor protein related to ezrin-radixin-moesin that modulates the activity of PI3K/AKT, Raf/MEK/ERK, and mTOR signaling pathways. In contrast, molecular insights on the different forms of SWN remain unclear. Inactivating mutations in the tumor suppressor genes SMARCB1 and LZTR1 are considered responsible for a majority of cases. Recently, treatment strategies to target specific genetic or molecular events involved in their tumorigenesis are developed. This study discusses molecular pathways and related targeted therapies for NF1, NF2, and SWN and reviews recent clinical trials which involve NF patients.

National Trends in Surgical Resection of Vestibular Schwannomas

OBJECTIVE

To characterize the national trend for surgical resection of vestibular schwannoma (VS) and to assess changes in demographics, length of stay (LOS), discharge patterns, and hospital charges.

STUDY DESIGN

Population-based inpatient registry analysis.

SETTING

National Inpatient Sample and SEER database (Surveillance, Epidemiology, and End Results).

PATIENTS AND METHODS

Retrospective review of the US National Inpatient Sample and the SEER database from 2001 to 2014 of all patients who underwent resection of VS.

RESULTS

A total of 24,380 VS resections were performed. While the annual incidence of VS remained stable at 1.38 per 100,000, surgical volume declined by 36.1%, from 2807 in 2001 to 1795 in 2014 (R² = 0.58). Total hospital charges more than doubled, from $52,475 in 2001 to $115,164 in 2014 ($4478 per year, R² = 0.96). While most procedures were performed at large-sized hospitals, this decreased from 89% in 2002 to 75.8% in 2014. Average LOS remained stable at 5.2 days during the study period. The number of discharges to a nursing facility increased from 113 (5.5%) in 2002 to 245 (13.6%) in 2014 (P = .0002).

CONCLUSION

VS resection has evolved in the United States. While the incidence remained stable, surgical volume decreased by 36%, and hospital charges more than doubled. More cases are being performed at smaller hospitals. Although LOS did not vary significantly, there is an increase in nonroutine discharges. These data may guide future research in resource utilization in neurotology.

Difference in the hypoxic immunosuppressive microenvironment of patients with neurofibromatosis type 2 schwannomas and sporadic schwannomas

BACKGROUND

Neurofibromatosis type 2 (NF2) patients uniformly develop multiple schwannomas. The tumor-microenvironment (TME) is associated with hypoxia and consists of immunosuppressive cells, including regulatory T cells (Tregs) and tumor-associated macrophages (TAMs). The hypoxic TME of NF2 schwannomas remains unclear. In addition, no comparative study has investigated immunosuppressive cells in NF2 and sporadic schwannomas.

METHODS

In 22 NF2 and 21 sporadic schwannomas, we analyzed the immunohistochemistry for Ki-67, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor receptor 1 (VEGFR1) and VEGFR2, platelet derived growth factor receptor-beta (PDGFR-β), programmed cell death-1 (PD-1)/ programmed cell death ligand-1 (PD-L1), Foxp3, CD163, CD3, and CD8 to assess the immunosuppressive TME.

RESULTS

Most vessels in sporadic schwannomas exhibited slight or negative VEGFR1 and 2 expressions with pericytes coverage. In contrast, large vessels in NF2 schwannomas exhibited strong VEGFR1 and 2 expressions without pericytes. The number of CD3⁺, CD8⁺, and CD163⁺ cells was significantly higher in NF2 schwannomas than in sporadic ones. The expression of PD-L1 and nestin positive cell ratio was higher in NF2 schwannomas than that in sporadic ones. The number of CD163⁺ cells, nestin positive cell ratio, and HIF-1α expression were significantly associated with shorter progression-free survival in NF2 schwannomas.

CONCLUSIONS

This study presents the clinicopathological features of the differences in immunosuppressive cells and the expression of immune checkpoint molecules between NF2 and sporadic schwannomas. Hypoxic TME was first detected in NF2-schwannomas, which was associated with the tumor progression.

A VEGF receptor vaccine demonstrates preliminary efficacy in neurofibromatosis type 2

The anti-VEGF antibody bevacizumab has shown efficacy for the treatment of neurofibromatosis type 2 (NF2). Theoretically, vascular endothelial growth factor receptors (VEGFRs)-specific cytotoxic T lymphocytes (CTLs) can kill both tumor vessel cells and tumor cells expressing VEGFRs. Here we show an exploratory clinical study of VEGFRs peptide vaccine in seven patients with progressive NF2-derived schwannomas. Hearing improves in 2/5 assessable patients (40%) as determined by international guidelines, with increases in word recognition scores. Tumor volume reductions of ≥20% are observed in two patients, including one in which bevacizumab had not been effective. There are no severe adverse events related to the vaccine. Both VEGFR1-specific and VEGFR2-specific CTLs are induced in six patients. Surgery is performed after vaccination in two patients, and significant reductions in the expression of VEGFRs in schwannomas are observed. Therefore, this clinical immunotherapy study demonstrates the safety and preliminary efficacy of VEGFRs peptide vaccination in patients with NF2.

The anti-vascular endothelial growth factor (VEGF) antibody bevacizumab has shown efficacy for the treatment of neurofibromatosis type 2 (NF2). Here, the authors show that VEGFRs peptide vaccination can improve hearing and reduce tumor volume in NF2 patients, including in previously bevacizumab resistant tumors.

Preoperative Assessment of Cervical Vestibular Evoked Myogenic Potentials (cVEMPs) Help in Predicting Hearing Preservation After Removal of Vestibular Schwannomas Through a Middle Fossa Craniotomy

OBJECTIVE

To determine whether cervical vestibular evoked myogenic potentials (cVEMPs) are predictive of hearing preservation in patients undergoing vestibular schwannoma removal through middle fossa craniotomy approach.

STUDY DESIGN

Retrospective case study.

SETTING

Tertiary referral center.

PATIENTS

Eighteen patients who underwent a middle fossa craniotomy for vestibular schwannoma (stage I or II of Koos classification) with attempted hearing preservation from January 2008 to February 2016 were retrospectively reviewed.

INTERVENTION

Pre-surgical cVEMPs test, videonystagmography (caloric test), and magnetic resonance imaging (MRI) as well as a pre- and post-surgical audiometry test.

MAIN OUTCOME MEASURES

cVEMPs parameters including amplitude asymmetry ratio (AR), P13, and N23 latencies and peak-to-peak amplitude between P13 and N23 waves were calculated. Hearing data were classified according to the AAO-HNS hearing classes. The nerve of origin of the tumor was specified during surgery and the largest tumor diameter was measure on MRI axial plane on T2-CISS weighed images.

RESULTS

Preoperative amplitude asymmetry ratio was lower (n = 15, Mann-Whitney U test, p < 0.001) in the group with postoperative hearing preservation (n = 11) compared with the group with postoperative hearing preservation failure (n = 4). The positive predictive value of an AR less than 24% to assess postoperative hearing preservation is 91.6%. Tumor size and localization were not correlated with cVEMPs, nor with caloric testing in this group of small-sized intracanalicular vestibular schwannomas.

CONCLUSIONS

Our data suggest that cVEMPs may help predict hearing preservation outcome in vestibular schwannoma surgery via the middle fossa craniotomy approach.

Hearing Response Following Internal Auditory Canal Decompression in Neurofibromatosis Type 2

BACKGROUND

Hearing response following an osteodural decompression of the internal auditory canal (IAC) is controversial.

OBJECTIVE

To evaluate the course of auditory brainstem responses (ABRs) and the early hearing response during the first year following IAC decompression for small to medium-sized vestibular schwannomas occurring in neurofibromatosis type 2 (NF2).

METHODS

Retrospective chart review of middle fossa craniotomy for IAC osteodural decompression in NF2-related vestibular schwannomas.

RESULTS

Twelve NF2 patients were operated on from 2011 to 2016 for IAC decompression. All had NF2 according to the Manchester criteria. All had a progressive change of their ABRs documented from the diagnosis of NF2 over a mean period of 6.25 [0.36;10.9] yr. Treatment was proposed to stop hearing progression based on the speech discrimination scores (SDSs; n = 4) or for hearing maintenance (n = 8). In patients with prior hearing progression, hearing responses were observed in 3 of the 4 patients during the first year. One patient kept on progressing. In the hearing maintenance group, the SDSs remained stable. SDSs improved from 85% [20-100] to 92.5% [60-100] on average (n = 12) and from 55% [20-80] to 77.5% [50-100] in the hearing progression group (n = 4). ABRs improved in 4 patients following decompression.

CONCLUSION

IAC decompression allows early objective hearing responses in select patients. We suggest that the procedure should be offered to patients with hearing progression based on their SDSs and/or associated progressive increases in their wave III and V latencies on ABRs.

Natural History of Sporadic Vestibular Schwannoma: A Volumetric Study of Tumor Growth

Objective

(1) Assess 3-dimensional volumetric growth of untreated sporadic vestibular schwannomas (VSs) in a large cohort of patients treated with conservative observation. (2) Compare volumetric and conventional linear diameter measurements for detecting tumor growth.

Study Design

Case series with chart review.

Setting

Tertiary skull base referral center.

Subjects and Methods

Patients with sporadic VS who elected initial conservative treatment with at least 2 serial magnetic resonance imaging (MRI) scans were included. Tumor volume was determined with 3-dimensional segmentation of MRI sequences. The volumetric threshold for tumor growth was an increase ≥20% from baseline tumor volume. Tumor size based on linear diameter was assessed with the 1995 American Academy of Otolaryngology—Head and Neck Surgery Foundation guidelines for VS outcome reporting, with growth defined as an increase ≥2 mm.

Results

A total of 361 patients were included with a median radiologic follow-up of 4.1 years (interquartile range [IQR], 2.5-6.8). At diagnosis, 232 VSs (64%) were purely intracanalicular, and 129 (36%) extended into the cerebellopontine angle. The median baseline tumor volume was 0.161 cm3 (IQR, 0.054-0.418). Overall, 69% of tumors demonstrated volumetric growth at a median of 1.1 years (IQR, 0.6-2.1) after initial MRI. In contrast, based on linear measurement assessment, 48% of tumors demonstrated growth at a median of 1.8 years (IQR, 0.8-3.1) from first MRI scan. Disequilibrium, facial hypoesthesia, aural fullness, initial tumor size, and nonincidental diagnosis were associated with tumor growth.

Conclusion

Three-dimensional volumetric assessment of VS provides a more sensitive measure of tumor growth when compared with linear diameter assessment. Through volumetric analysis, the current study revealed that a significant proportion of VSs demonstrate growth during observation.