ATRT-03. PRIMARY DIFFUSE LEPTOMENINGEAL ATYPICAL TERATOID/RHABDOID TUMOR (ATRT) OF CHILDHOOD DEMONSTRATING UNEXPECTED IMPROVEMENT UPON CESSATION OF CONVENTIONAL THERAPY FOR PRESUMED PROGRESSION; A MOLECULARLY CHARACTERIZED CASE REPORT

Abstract

Abstract BACKGROUND Atypical teratoid/rhabdoid tumors (ATRTs) are malignant tumors of the central nervous system, typically presenting in the posterior fossa of very young children. Prognosis remains poor despite current therapy, while tumorigenesis implicates both genomic and epigenetic dysregulation. Primary diffuse leptomeningeal disease (PDL ATRT), without a defined intraparenchymal lesion, is an extremely rare ATRT variant with only seven cases reported. None of these preceding cases had undergone molecular characterization. We compared our case, who demonstrated an atypical clinical and radiological trajectory, against these seven cases. CASE PRESENTATION We describe a PDL ATRT, with hitherto novel molecular and imaging characteristics, in a pediatric patient who subsequently demonstrated radiological and clinical recovery from radiologically diagnosed metastatic relapse in the absence of conventional ATRT salvage treatment. Our case is the first to utilize Magnetic Resonance Imaging Arterial Spin Labelling perfusion imaging to suggest an underlying malignancy as the responsible etiology for this patient’s complex presentation, and the first to use methylation profiling to establish a tumor molecular subgroup for a PDL ATRT patient (identifying a MYC-subgroup in this case). CONCLUSIONS For this reported case of pediatric MYC-subgroup PDL ATRT, MR perfusional imaging aided in establishing the diagnosis and predicting potential relapse as part of a multi-parametric imaging assessment. We administered upfront intensive multimodal therapy, including high-dose CSRT to the patient, resulting in the longest overall survival for any patient reported with this extremely challenging ATRT variant. His unanticipated clinical and radiological improvement following a subsequent radiological diagnosis of tumor relapse highlights the importance of confirming recurrence by tissue extraction where feasible, but suggests that further evaluation of histone deacetylase inhibition as a potential future therapy in ATRT is warranted.