Choroid plexus carcinomas and rhabdoid tumors: Phenotypic and genotypic overlap

Five of six poorly differentiated choroid plexus carcinomas identified at o ur institution contained cells displaying a rhabdoid phenotype. Immunoperox idase stains showed focal positivity for cytokeratin, epithelial membrane a ntigen, glial fibrillary acidic protein, S100, and vimentin. The MIB-1 prol iferative index ranged from 7.0% to 27.1%. All six tumors were p53 positive . Only the one child with Li-Fraumeni syndrome had a p53 germline mutation. Electron microscopy verified choroid plexus differentiation and the co-exi stence of rhabdoid cells. Of the five studied, four had deletions of chromo some 22 [three with monosomy 22 and one with del(22)(q12)]. Thus, there was a phenotypic and genotypic overlap between choroid plexus carcinomas and r habdoid tumors.