ATRT-11. Anatomico-biological correlations define a new layer for ATRT molecular subgroups pointing to potential lineages of origin

Atypical teratoid rhabdoid tumors (ATRT) are divided in three molecular subgroups, the so-called MYC, TYR and SHH subgroups. This heterogeneity suggests some diversity in the cells of origin, which remain hypothetical thus far. A careful radiological review of 55 MRI at diagnosis was performed in parallel with a careful analysis of mouse tumor origin in the Rosa26-CreERT2::Smarcbflox/flox model. Methylation, bulk RNAseq and scRNAseq analyses were integrated to these anatomic information to highlight potential origin for each molecularly and anatomically defined subgroups. We demonstrated that mouse Myc-ATRTs derive from extra-parenchymal meningeal areas, a finding consistant with many human MYC ATRT being clearly of intra-cranial extra-axial origin. Although this finding could point to a neural crest origin, transcriptomic features fail to unravel any lineage-specific signature. We also defined a distinct supra-tentorial SHH ATRT subgroup, characterized both in mouse and Humans by neural features pointing to the ganglionic eminence progenitors as the candidate origin. Finally we identified a distinct infra-tentorial SHH ATRT subgroup, not observed in mice, with hindbrain/midbrain boundary progenitor signature. scRNAseq from human SHH infra-tentorial tumors consistently suggest a dedifferentiation process involving the Notch pathway in the oncogenic transformation of hindbrain/midbrain neural progenitors.