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Abstract Background Rare pediatric and young adult brain tumors pose major diagnostic and therapeutic challenges due to limited evidence and scattered expertise. The International Rare Brain Tumor Board was established to enable multidisciplinary case review, shared learning, and collaborative decision support. Methods Launched in February 2025, the Rare Brain Tumor Board is a monthly collaborative initiative led by Children’s National Hospital and the National Institutes of Health (NIH). Close partnership with the European Pediatric Rare CNS Tumor Board enhances transatlantic exchange and alignment of diagnostic and treatment recommendations. De-identified cases are presented with clinical history, neuroimaging, histopathology, and molecular profiling, including DNA methylation classification, available for the majority of cases. Sessions are structured to support integrated diagnosis and evidence-informed management recommendations through multidisciplinary discussion (neuropathology, neuroradiology, neurosurgery, radiation oncology, and pediatric as well as adult neuro-oncology). Findings Since its inception, 12 sessions have been held averaging 138 participants per session, reviewing a total of 32 cases (mean 3 cases/session; range 1–4) from 7 different countries and 3 different continents. Entities reviewed include DICER1-intracranial sarcoma (n = 5), astroblastoma (n = 4), FOXR2-activated neuroblastoma (n = 4), CNS tumors with BCOR internal tandem duplication (n = 3) and, BCOR-fused tumors (n = 3), CIC-rearranged-sarcoma (n = 3), intracranial mesenchymal tumor FET::CREB fusion positive (n = 3), MN1::PATZ1 fusion tumors (n = 2), undifferentiated sarcoma (n = 2), PLAG1-fusion tumor (n = 1), medullomyoblastoma (n = 1), and EZHIP-altered diffuse midline glioma (DMG) (n = 1). Multidisciplinary review has supported diagnostic clarification, strengthened familiarity with ultra-rare entities, and informed real-world treatment discussions in settings where prospective data are limited. Discussions have also increased awareness of rare brain tumor registries and opportunities for systematic case capture. Conclusion An international multidisciplinary rare brain tumor board is a feasible, scalable model to advance integrated diagnosis and collaborative management of ultra-rare pediatric and young adult brain tumors, while building a shared knowledge base across institutions.

BACKGROUND AND OBJECTIVES: Pediatric large-volume brain arteriovenous malformations (AVMs) carry a substantial lifelong hemorrhage risk, neurological symptoms, and treatment morbidity. Single-session stereotactic radiosurgery (SRS) is often unsuitable due to constraints on dose-volume toxicity. Volume-staged SRS (VS-SRS) enables sequential dosing of large nidus volumes, potentially enhancing safety while maintaining efficacy. Evidence in children remains limited. We aimed to evaluate outcomes of VS-SRS for large AVMs in pediatric patients. METHODS: A multicenter retrospective cohort was assembled from 21 centers, including patients aged younger than 21 years treated with VS-SRS for AVMs >10 cm 3 . Clinical and radiological end points included obliteration, hemorrhage, and permanent symptomatic radiation-induced changes (RIC). RESULTS: A total of 103 patients were included (median age 14 years; IQR, 12-17). The median nidus volume at first stage was 18.2 cm 3 (IQR, 12.3-25.6). Median prescription dose per stage was 17 Gy (IQR, 16-18). The median clinical follow-up from the first stage was 57.5 months (IQR, 25-138). Obliteration occurred in 42 of 103 patients (40.8%), with actuarial rates of 6.9% (95% CI: 2.8-14) at 3 years and 29% (95% CI: 20-39) at 5 years. Hemorrhage occurred in 17 of 103 patients (16.5%) during follow-up, and permanent RIC was observed in 9 of 103 patients (8.7%). CONCLUSION: VS-SRS is a reasonably safe, selected option for pediatric large-volume AVMs when microsurgical or endovascular cure is not feasible or prudent. Delivering ≥17 Gy per stage while limiting each treatment volume to <15 cm 3 supports durable nidus control with acceptable toxicity. VS-SRS represents a key modality in multidisciplinary management of this historically difficult-to-treat population.

OBJECTIVE Ruptured, large pediatric arteriovenous malformations (AVMs) pose a significant management challenge due to high rerupture risk and the morbidity of conventional treatments. Volume-staged stereotactic radiosurgery (VS-SRS) has emerged as an alternative; however, evidence for its use in this specific population is limited. This study aimed to evaluate the long-term efficacy and safety of VS-SRS for ruptured, large AVMs in a dedicated pediatric cohort. METHODS This international, multicenter, retrospective cohort study from 21 centers analyzed outcomes for 42 pediatric patients (age < 18 years) with previously ruptured, large AVMs treated with VS-SRS. The primary outcome was complete AVM obliteration, and secondary outcomes included post-SRS hemorrhage, radiation-induced changes (RICs), and favorable outcome. Favorable outcome in this study was defined as obliteration without post-SRS hemorrhage or permanent RIC. RESULTS At the initial SRS, the median patient age was 14.5 years, and the median AVM volume was 15.0 cm 3 ; most AVMs were high grade (Spetzler-Martin grades IV and V). With a median follow-up of 41.5 months, complete AVM obliteration was achieved in 21 patients (50.0%). The cumulative obliteration rate was 37% at 5 years and 56% at 10 years. Patients with a nidus volume of ≤ 10 cm 3 had significantly higher cumulative obliteration rates than those with a nidus volume > 10 cm 3 (log-rank test, p = 0.021). Similarly, patients treated with a prescription dose > 17 Gy showed significantly higher cumulative obliteration rates compared to those treated with a dose ≤ 17 Gy (log-rank test, p = 0.012). The cumulative 5-year incidences of hemorrhage and RICs following VS-SRS were 19% and 7%, respectively. In multivariable analysis, only larger total AVM volume was an independent predictor of a lower likelihood of favorable outcome (hazard ratio 0.89, 95% CI 0.80–0.99; p = 0.036). CONCLUSIONS In this multicenter pediatric cohort, VS-SRS for ruptured, large AVMs provides a reasonable chance of long-term obliteration, but generally acceptable risks of post-SRS hemorrhage and RICs exist. VS-SRS should be considered as an option for pediatric patients with large, ruptured AVMs.

BACKGROUND AND OBJECTIVES: Stereotactic radiosurgery (SRS) for brain arteriovenous malformations (AVMs) can cause radiation-induced changes (RIC), but its interactions with AVM embolization are not well established. The aim of this study was to assess the effect of previous embolization on RIC in SRS-treated AVM patients. METHODS: Data of AVM patients treated with single-session SRS from 1987 to 2018 were retrieved from the International Radiosurgery Research Foundation. Univariable and stepwise backward logistic regression models were used to identify RIC predictors. Patients were stratified into those who received pre-SRS embolization (E + SRS) vs those who did not (SRS-only). Radiologic RIC (rRIC) was the primary end point. Secondary outcomes included symptomatic RIC (sRIC) and permanent symptomatic RIC (pRIC). RESULTS: Among 1187 AVM patients, the mean age was 36.4 years (SD 16.8), with 50.4% female patients. AVMs had a mean untreated AVM volume of 5.2 cm 3 . A total of 130 patients (11%) underwent neoadjuvant embolization (E + SRS). The overall rRIC and sRIC rates were 32.8% and 12.1%, respectively, with time to rRIC and sRIC being significantly longer in the E + SRS vs SRS-only cohorts (103.6 ± 339.4 vs 11.3 ± 12.5 and 60.4 ± 262.9 vs 9.5 ± 9.0 months, respectively). Seizures at presentation and ≥3-cm untreated AVM volume significantly correlated with a higher likelihood of rRIC (adjusted odds ratio [aOR] 2.32 [1.25-4.30] and aOR 2.77 [1.24-6.16], respectively). Age and pre-SRS embolization were associated with a significantly lower risk of rRIC (aOR 0.97 [0.96-0.99] and aOR 0.32 [0.13-0.74], respectively). The E + SRS cohort had significantly reduced odds of rRIC (aOR = 0.37 [0.15-0.89]) and pRIC (aOR = 0.04 [0.00-0.30]) after adjusting for significant covariates. CONCLUSION: Seizures at presentation and larger untreated AVM volume were independently associated with an increased risk of rRIC, whereas older age and pre-SRS embolization were protective. Notably, patients who underwent embolization before SRS had lower odds of rRIC and pRIC, with delayed onset of complications compared with SRS-only.

BACKGROUND AND OBJECTIVES: Single-session stereotactic radiosurgery (SRS) has limited role for large arteriovenous malformations (AVM). Volume-staged SRS (VS-SRS) is used to optimize outcomes, but studies reporting results are limited. METHODS: This multicenter retrospective cohort of 378 patients from 21 centers reports results of VS-SRS for the entire AVM nidus. We report favorable outcome, obliteration, hemorrhage, and permanent symptomatic adverse radiation effect rates. RESULTS: The median age was 31 years (IQR: 19-44) at the first volume stage, with patients treated in 2–4 stages. The median total nidus volume was 21 cm 3 (IQR: 13.9-30.1 cm 3 ), and a median prescription dose of 17 Gy (IQR: 16-18 Gy) was used. The median radiographic and clinical follow-up were 48 and 55 months, respectively. Seventy-seven patients (20.4%) had a favorable outcome, with the 3-year and 5-year rates being 3.9% and 18%, respectively. 127 patients (33.6%) achieved obliteration, with the 3-year and 5-year rates being 6.8% and 26%, respectively. Obliteration rates of AVMs <15 cm 3 were 81% and 31%, respectively. The latency period hemorrhage incidence rate was 3.02 cases per 100 patient-years; 52 patients (13.8%) had a bleed. Seventy-two patients (19%) had symptomatic adverse radiation effect; in 38 patients (10.1%), these were permanent. Total nidus volume, prescription dose at first stage, diffuse nidus, and prior hemorrhage were all independent affecting outcome rates. CONCLUSION: VS-SRS can be used to treat large AVMs as a standalone treatment. Obliteration rates and favorable outcomes are lower than that with smaller AVMs, and repeat treatment is often required. Optimizing treatment plans, by increasing prescription doses, reducing treatment volume at each stage, and increasing the number of stages, may lead to better outcomes.

Background Given the low haemorrhagic risk of intracranial low-grade dural arteriovenous fistulas (dAVFs), the benefits of routine intervention remain controversial. This study compares patient outcomes treated with stereotactic radiosurgery (SRS) versus conservative management. Method Multicentre retrospective analysis of the Consortium for Dural Arteriovenous Fistula Outcomes Research and the International Radiosurgery Research Foundation data. Inclusion criteria were (1) intracranial low-grade dAVF diagnosed by catheter-based angiography, (2) no prior dAVF-related haemorrhage and (3) management with upfront SRS (intervention group) or conservative management (observation group). The primary outcome was symptomatic improvement. Secondary outcomes included dAVF obliteration, up-conversion, haemorrhage, improvement and favourable modified Rankin Scale (mRS) at follow-up. Results 304 patients with a mean age of 56 years (SD 13.5) and a follow-up of 46.7 months (SD 45.5) were included. 135 (44.4%) were managed conservatively and 169 (55.6%) had upfront SRS. Compared with the observation group, symptomatic and mRS Score improvement (≥1-point decrease in baseline score) was more likely in the intervention group (95.1% vs 58.5%; OR=13.75 (5.61–33.69) and 37.0% vs 24.0%; OR=1.85 (1.09–3.15), respectively). These findings remained significant after multiple imputation and propensity score matching. Remaining outcomes were similar between groups. The all-cause mortality rate was 5.4% (n=16), unrelated to the dAVF or treatment. Five (3.0%) SRS-related complications were reported and resolved during the follow-up period. Conclusions SRS was associated with increased symptomatic and mRS Score improvement for low-grade dAVFs compared with conservative management. SRS had a low complication risk and did not appear to alter dAVF obliteration or haemorrhage. Future prospective trials on SRS as a first-line intervention for symptomatic low-grade dAVFs should be considered.

OBJECTIVE This study aimed to evaluate local control (LC) of tumors, patient overall survival (OS), and the safety of stereotactic radiosurgery (SRS) for esophageal cancer brain metastases (EBMs). METHODS This retrospective cohort study used data from 15 International Radiosurgery Research Foundation facilities encompassing 67 patients with 185 EBMs managed using SRS between January 2000 and May 2022. The median patient age was 63 years, with a male predominance (92.5%). Most patients (64.2%) had a single brain metastasis, while 7.5% had more than 5 metastases. The median tumor volume was 0.9 cm 3 , and the median margin dose delivered to the tumor was 20 Gy. RESULTS The median OS post-SRS was 15.2 months, with 1- and 2-year OS rates of 65.7% and 32.3%, respectively. A significant inverse correlation was found between the number of EBMs and OS in the univariable analysis. LC rates at 1 and 2 years were 89% and 76%, respectively. Adverse radiation effects (AREs) were observed in 17.9% of patients, with 13.4% being mild and transient and 4.5% severely symptomatic (Common Terminology Criteria for Adverse Events grade 3). New intracranial disease developed in 58.2% of patients, with 1- and 2-year rates of 58% and 73%, respectively. CONCLUSIONS SRS for EBMs demonstrated high survival rates and effective tumor control, with a low incidence of severe AREs. These findings highlight the potential role of SRS in the multidisciplinary multimodality management paradigm of EBM.

BACKGROUND AND OBJECTIVES: Stereotactic radiosurgery (SRS) with neoadjuvant embolization is a treatment strategy for brain arteriovenous malformations (AVMs), especially for those with large nidal volume or concomitant aneurysms. The aim of this study was to assess the effects of pre-SRS embolization in AVMs with an associated intracranial aneurysm (IA). METHODS: The International Radiosurgery Research Foundation AVM database from 1987 to 2018 was retrospectively reviewed. SRS-treated AVMs with IAs were included. Patients were categorized into those treated with upfront embolization (E + SRS) vs stand-alone SRS (SRS). Primary end point was a favorable outcome (AVM obliteration + no permanent radiation-induced changes or post-SRS hemorrhage). Secondary outcomes included AVM obliteration, mortality, follow-up modified Rankin Scale, post-SRS hemorrhage, and radiation-induced changes. RESULTS: Forty four AVM patients with associated IAs were included, of which 23 (52.3%) underwent pre-SRS embolization and 21 (47.7%) SRS only. Significant differences between the E + SRS vs SRS groups were found for AVM maximum diameter (1.5 ± 0.5 vs 1.1 ± 0.4 cm 3 , P = .019) and SRS treatment volume (9.3 ± 8.3 vs 4.3 ± 3.3 cm 3 , P = .025). A favorable outcome was achieved in 45.4% of patients in the E + SRS group and 38.1% in the SRS group ( P = .625). Obliteration rates were comparable (56.5% for E + SRS vs 47.6% for SRS, P = .555), whereas a higher mortality rate was found in the SRS group (19.1% vs 0%, P = .048). After adjusting for AVM maximum diameter, SRS treatment volume, and maximum radiation dose, the likelihood of achieving favorable outcome and AVM obliteration did not differ between groups ( P = .475 and P = .820, respectively). CONCLUSION: The likelihood of a favorable outcome and AVM obliteration after SRS with neoadjuvant embolization in AVMs with concomitant IA seems to be comparable with stand-alone SRS, even after adjusting for AVM volume and SRS maximum dose. However, the increased mortality among the stand-alone SRS group and relatively low risk of embolization-related complications suggest that these patients may benefit from a combined treatment approach.

Abstract Purpose To report patient outcomes and local tumor control rates in a cohort of patients with biopsy-proven HER-2 positive breast cancer treated with stereotactic radiosurgery (SRS) for brain metastases (BM). Methods This international, retrospective, multicenter study, included 195 female patients with 1706 SRS-treated BM. Radiologic and clinical outcomes after SRS were determined and prognostic factors identified. Results At SRS, median patient age was 55 years [interquartile range (IQR) 47.6–62.0], and 156 (80%) patients had KPS ≥ 80. The median tumor volume was 0.1 cm3 (IQR 0.1–0.5) and the median prescription dose was 16 Gy (IQR 16–18). Local tumor control (LTC) rate was 98%, 94%, 93%, 90%, and 88% at six-, 12-, 24-, 36- and 60-months post-SRS, respectively. On multivariate analysis, tumor volume (p = < 0.001) and concurrent pertuzumab (p = 0.02) improved LTC. Overall survival (OS) rates at six-, 12-, 24-, 36-, 48-, and 60-months were 90%, 69%, 46%, 27%, 22%, and 18%, respectively. Concurrent pertuzumab improved OS (p = 0.032). In this patient subgroup, GPA scores ≥ 2.5 (p = 0.038 and p = 0.003) and rare primary tumor histologies (p = 0.01) were associated with increased and decreased OS respectively. Asymptomatic adverse radiation events (ARE) occurred in 27 (14.0%) and symptomatic ARE in five (2.6%) patients. Invasive lobular carcinoma primary (p = 0.042) and concurrent pertuzumab (p < 0.001) conferred an increased risk for overall but not for symptomatic ARE. Conclusion SRS affords effective LTC for selected patients with BM from HER-2 positive breast cancer. Concurrent pertuzumab improved LTC and OS with however an increased risk for overall but not symptomatic ARE.

Abstract Despite advances in understanding the genetic abnormalities in myeloproliferative neoplasms (MPN) and the development of JAK2 inhibitors, there is an urgent need to devise new treatment strategies, particularly for patients with triple-negative (TN) myelofibrosis (MF) who lack mutations in the JAK2 kinase pathway and have very poor clinical outcomes. Here we report that MYC copy number gain and increased MYC expression frequently occur in TN-MF and that MYC-directed activation of S100A9, an alarmin protein that plays pivotal roles in inflammation and innate immunity, is necessary and sufficient to drive development and progression of MF. Notably, the MYC-S100A9 circuit provokes a complex network of inflammatory signaling that involves numerous hematopoietic cell types in the bone marrow microenvironment. Accordingly, genetic ablation of S100A9 or treatment with small molecules targeting the MYC-S100A9 pathway effectively ameliorates MF phenotypes, highlighting the MYC–alarmin axis as a novel therapeutic vulnerability for this subgroup of MPNs. Significance: This study establishes that MYC expression is increased in TN-MPNs via trisomy 8, that a MYC-S100A9 circuit manifest in these cases is sufficient to provoke myelofibrosis and inflammation in diverse hematopoietic cell types in the BM niche, and that the MYC-S100A9 circuit is targetable in TN-MPNs.