Synchronous rosette-forming glioneuronal tumor and diffuse astrocytoma with molecular characterization: a case report.

Rosette-forming glioneuronal tumor (WHO grade I) is a rare neoplasm primarily arising in young adults that is characterized by distinctive neurocytic rosette formation, a spindled glial component resembling pilocytic astrocytoma, and a high incidence of PIK3CA mutation. Low-grade diffuse astrocytoma (WHO grade II), on the other hand, is far more common and is characterized by a high incidence of IDH mutation. Here we report a patient with simultaneous presentation of a midbrain-cerebellar rosetteforming glioneuronal tumor and a cerebral diffuse astrocytoma. Molecular characterization of both tumors confirmed characteristic, mutually exclusive, distinct signatures, with the rosette-forming glioneuronal tumor exhibiting a previously unreported novel PIK3CA gene mutation.