Sellar region neurocytomas exhibit a CIMP and neuroendocrine-like epigenetic signature distinct from other intra-axial neurocytomas.

Sellar region neurocytoma (SELN) is a rare neoplasm whose relationship to other neurocytomas within the central nervous system (CNS) has remained unclear. Prior reports have variably classified SELN as a variant of extraventricular neurocytoma (EVN), while immunohistochemical and ultrastructural studies have suggested a hypothalamic origin. Here, we performed unsupervised clustering of DNA methylation data across a large pan-cancer reference set and identified SELN (n = 20) as distinct from other neurocytomas and regional mimics, as well as clustering with neuroendocrine tumors from other organ sites. SELN exhibited a CIMP-like phenotype, TTF1 negativity (0/8), and AVP (vasopressin) promoter hypomethylation, implicating a magnocellular hypothalamic cell of origin. In evaluable cases, a neuronal/neuroendocrine immunophenotype was observed (synaptophysin 8/8, chromogranin A 5/5) with absent pituitary transcription factor expression (PIT1 and TPIT negative 0/4). DNA sequencing (n = 5) and RNA-based fusion profiling (n = 4) did not detect recurrent mutations or gene fusions, respectively. Patients often presented with visual disturbances or headaches and spanned pediatric and older age groups (median 42 years, range 12.5-75), with no sex predilection. Despite locally aggressive imaging features in some cases (cavernous sinus invasion, carotid encasement, hydrocephalus), disease-free survival (n = 13) was comparable to central neurocytoma, with no disease-related deaths during the limited follow-up. Together, these findings support SELN as a molecularly distinct hypermethylated neuroendocrine-like epitype and clinicopathologic entity.