Chi, Susan N

Abstract Response Assessment in Pediatric Neuro-Oncology (RAPNO) is an international working group dedicated to developing standardized recommendations for response assessment in children with central nervous system tumors enrolled on clinical trials. This standardization facilitates easier and more reliable comparison of responses across trials. Since the first RAPNO publication in 2013, response guidelines have been issued for medulloblastoma (MB), low-grade glioma (LGG), high-grade glioma (HGG), diffuse intrinsic pontine glioma, ependymoma, and craniopharyngioma. Many of these guidelines have already been incorporated into clinical trials to evaluate their effectiveness and accuracy. RAPNO has always been predicated on the idea that these consensus recommendations will require updates over time as they are applied in practice given technological advancements, evolving treatment approaches, and growing knowledge of disease pathology. A half-day RAPNO symposium sponsored by the Society of Neuro-Oncology was held in San Diego, California, United States, on May 15, 2025. This event coincided with the 8th Biennial Pediatric Society of Neuro-Oncology meeting. The main objectives were to identify ongoing RAPNO challenges, discuss potential updates, and plan future initiatives across 3 specific groups: (1) LGG/Craniopharyngioma, (2) HGG/diffuse midline glioma (DMG)/Ependymoma, and (3) MB and other seeding tumors. This manuscript reviews the symposium proceedings and highlights key topics and challenges discussed, as well as outlining future RAPNO initiatives.

Abstract Background National Cancer Institute-Children’s Oncology Group Pediatric Molecular Analysis for Therapy Choice assigns patients aged 1-21 years with refractory solid tumors, brain tumors, lymphomas, and histiocytic disorders to phase II trials of molecularly targeted therapies based on detection of predefined genetic alterations. Patients whose tumors harbored EZH2 mutations or loss of SMARCB1 or SMARCA4 by immunohistochemistry were treated with EZH2 inhibitor tazemetostat. Methods Patients received tazemetostat for 28-day cycles until disease progression or intolerable toxicity (max 26 cycles). The primary endpoint was objective response rate; secondary endpoints included progression-free survival and tolerability of tazemetostat. Results Twenty patients (median age = 5 years) enrolled, all evaluable for response and toxicities. The most frequent diagnoses were atypical teratoid rhabdoid tumor (n = 8) and malignant rhabdoid tumor (n = 4). Actionable alterations consisted of SMARCB1 loss (n = 16), EZH2 mutation (n = 3), and SMARCA4 loss (n = 1). One objective response was observed in a patient with non-Langerhans cell histiocytosis with SMARCA4 loss (26 cycles, 1200 mg/m2/dose twice daily). Four patients with SMARCB1 loss had a best response of stable disease: epithelioid sarcoma (n = 2), atypical teratoid rhabdoid tumor (n = 1), and renal medullary carcinoma (n = 1). Six-month progression-free survival was 35% (95% confidence interval [CI] = 15.7% to 55.2%) and 6-month overall survival was 45% (95% CI = 23.1% to 64.7%). Treatment-related adverse events were consistent with prior tazemetostat reports. Conclusions Although tazemetostat did not meet its primary efficacy endpoint in this population of refractory pediatric tumors (objective response rate = 5%, 90% CI = 1% to 20%), 25% of patients with multiple histologic diagnoses experienced prolonged stable disease of 6 months and over (range = 9-26 cycles), suggesting a potential effect of tazemetostat on disease stabilization.