Abstract A015: Metastatic architecture in group 3-group 4 medulloblastoma reflects a developmental continuum that predicts therapeutic vulnerability

Abstract

Leptomeningeal metastasis is the leading cause of mortality for children with medulloblastoma, the most common malignant pediatric brain tumor. Metastatic disease displays striking morphological heterogeneity, ranging from discrete nodular deposits to diffused laminar layering of the spinal cord and the brain. Despite this architectural diversity, the biological mechanisms driving the distinct metastatic phenotypes and their therapeutic implications remain unknown. To address this knowledge gap, we utilized our novel metastasis-in-a-dish co-culture model in which medulloblastoma cells are grown on a layer of primary leptomeningeal cells under nutrient deprived conditions. Using this system, we have successfully recapitulated the morphological heterogeneity observed in patients with distinct metastatic patterns emerging across group 3 and group 4 medulloblastoma models. Using single cell RNA sequencing, we identified transcriptional programs uniquely associated with these divergent metastatic morphologies. Notably, we demonstrated that the observed phenotypic spectrum aligns with the previously described transcriptional continuum observed between group 3 and group 4 medulloblastoma. Laminar-like models demonstrated upregulation of progenitor-associated programs and MYC signaling, while nodular-like models were characterized by a more committed, neuronal transcriptional state. Functionally, these distinct metastatic phenotypes exhibited a differential response to chemotherapy, suggesting that the divergent metastatic architectures are biologically distinct entities with differential therapeutic susceptibilities. In conclusion, these findings support a model in which leptomeningeal metastasis represents a continuum of morphologically distinct states, each defined by transcriptionally and biologically divergent programs that shape therapeutic sensitivity.