Chromosome 22q dosage in composite extrarenal rhabdoid tumors: Clonal evolution or a phenotypic mimic?

Composite extrarenal rhabdoid tumors (CERTs) represent a diverse group of n eoplasms with rhabdoid shape in combination with one of several distinctive tumor types. Like the classic renal and extrarenal malignant rhabdoid tumo r (MRT), as well as the atypical teratoid/rhabdoid tumor (AT/RT) of the cen tral nervous system. CERTs typically show aggressive clinical behavior. Del etions and mutations of the INII gene on 22q11.2 have been identified in mo st classic MRTs and AT/RTs; however, it is not known whether the rhabdoid c omponents in CERTs have similar genetic abnormalities. Using fluorescence i n situ hybridization (FISH) on archival, paraffin-embedded tissue with a co mmercially available probe in close proximity to the INII locus (bcr), as w ell as other chromosome 22 probes, we studied 4 cases of MRT, 13 of AT/RT, and 16 of CERT (3 melanoma, 4 meningioma, 7 carcinoma, I rhabdomyosarcoma, and I neuroblastoma). Deletion of the 22q11.2 locus was demonstrated in 10 (77%) of 13 AT/RTs and 3 (75%) of 4 MRT, including 1 congenital MRT. Of the 16 CERTs, only 2 (a rhabdoid meningioma and a carcinoma with rhabdoid feat ures; 13%) harbored a deletion at this locus. This difference was statistic ally significant (P < .001). We conclude that deletion of 22q11.2, typical of most classic MRTs and AT/RTs, is infrequently seen in CERTs. This sugges ts that the rhabdoid component of CERTs does not evolve by way of the genet ic alteration characteristic of MRTs or AT/RTs, but represents instead a di stinct phenotype shared by a number of tumors as they undergo anaplastic pr ogression. Hum PATHOL 32:1102-1108. Copyright (C) 2001 by W.B. Saunders Com pany.