Rosette-forming glioneuronal tumor (RGNT)

RGNT presents in adolescents and adults, with tumors generally located infratentorially, although tumors can arise in mesencephalic or diencephalic regions.[68] The typical histological appearance shows both a glial component and a neurocytic component arranged in rosettes or perivascular pseudorosettes.[24] Outcome for patients with RGNT is generally favorable, consistent with the WHO grade 1 designation.[68]

DNA methylation profiling shows that RGNT has a distinct epigenetic profile that distinguishes it from other low-grade glial/glioneuronal tumor entities.[68] A study of 30 cases of RGNT observed FGFR1 hotspot variants in all analyzed tumors.[68] In addition, PIK3CA activating variants were concurrently observed in 19 of 30 cases (63%). Missense or damaging variants in NF1 were identified in 10 of 30 cases (33%), with 7 tumors having variants in FGFR1, PIK3CA, and NF1. The co-occurrence of variants that activate both the MAPK pathway and the PI3K pathway makes the variant profile of RGNT distinctive among astrocytic and glioneuronal tumors.