Aggressive Pediatric Primitive Round Cell Tumors with MN1::ZNF341 Fusion: A Mimic of Neuroblastoma.

Neuroblastoma is one of the most common tumors in young children, arising from the adrenal medulla or paraspinal sympathetic ganglia. We describe primitive round cell tumors presenting in three patients less than 1.5 years old, with striking clinical and pathologic similarities to neuroblastoma. Unlike neuroblastoma, however, these primitive tumors did not show specific histologic or immunophenotypic evidence of neuroblastic differentiation, and harbored a MN1::ZNF341 fusion. All patients progressed through neuroblastoma therapy and ultimately died of disease. These highly aggressive tumors mimicking neuroblastoma appear to be a novel and distinctive entity in need of further characterization.