Atypical teratoid rhabdoid tumor mimicking beta-catenin-positive nodular medulloblastoma

Excerpt

Atypical teratoid rhabdoid tumor (ATRT) is a rare and highly aggressive CNS tumor of early childhood. Until 2006 when INI-1 antibodies became commercially available, the diagnosis of ATRT was based on histological and immunophenotypical characteristics and then confirmed by cytogenetic analysis demonstrating monosomy 22 and recently, by SMARBC1/hSNF5/INI-1 bi-allelic inactivation [1]. The histological diagnosis remains challenging as rhabdoid cells, the key feature, may be lacking. The differential diagnosis of ATRT from other CNS tumors such as sPNET, medulloblastomas is difficult if it is based exclusively on histopathology and classical immunomarkers. INI-1 expression is very useful for confirming the diagnosis of ATRT and excellent concordance has been established between loss-of-function INI1 gene alterations and lack of INI-1 immunostaining [2]. Haberler et al [2] described eight classic medulloblastomas or sPNET with loss of INI-1 nuclear immunoreactivity. Consequently, it has been proposed that all CNS embryonal tumors should be tested for INI-1, except for classic desmoplastic/nodular medulloblastoma [2]. Indeed, the desmoplastic/nodular medulloblastoma subtype has never been described to be INI-1-negative or to include an ATRT component [2]. …