Sellar Atypical Teratoid/Rhabdoid Tumor (AT/RT): A Clinicopathologically and Genetically Distinct Variant of AT/RT

Atypical teratoid/rhabdoid tumors (AT/RTs) are rare aggressive tumors of the central nervous system that predominantly affect infants. Although adult AT/RT are rare, accumulated cases have revealed adult-specific AT/RT in the sellar region. Twelve previously reported cases of sellar AT/RT exclusively occurred in adult females, suggesting biological differences from conventional infant AT/RT. We herein investigated a series of 6 sellar AT/RT for histopathologic features, the molecular status of the INI1/SMARCB1 gene, and clinical courses. All 6 cases were adult females, ranging in age from 21 to 69 years old. Tumors were histologically characterized by a hemangiopericytoma-like stag-horn vasculature within a dense, diffuse proliferation of jumbled cells and a small number of scattered rhabdoid cells. This vascular pattern is not a common finding in AT/RT and appears to be a characteristic histology of sellar AT/RT. Biallelic alterations in the INI1 gene were identified by fluorescence in situ hybridization, direct sequencing, and multiple ligation-dependent probe amplification analyses in 4 of the 5 cases analyzed. Three of the 4 cases harbored 2 different mutations, presumably on different alleles (compound heterozygous mutations), and 1 case of which had a splice-site mutation. Combined with previous findings, the prevalence of compound heterozygous mutations and splice-site mutations was significantly higher in sellar AT/RT than in pediatric AT/RT. Sellar AT/RT represent a clinicopathologically and possibly genetically distinct variant of AT/RT showing a characteristic demography, different patterns of INI1 alterations, and a histology featured by a unique vasculature.