Pediatric extra-renal rhabdoid tumors with unusual morphology: A diagnostic pitfall for small biopsies

Rita Alaggio, Renata Boldrini, Benedetta Di Venosa, Angelo Rosolen, Gianni Bisogno, Gaetano Magro

Research output: Contribution to journalArticle


The diagnosis of malignant rhabdoid tumor (MRT) is straightforward if the typical, large eosinophilic rhabdoid cells are identified. We report on two diagnostically challenging cases of pediatric extra-renal MRTs which, when evaluated at incisional biopsy, were composed exclusively of small- to medium-sized round cells with focal spindling, lacking rhabdoid phenotype. This morphology, along with a polyphenotypic immunoprofile, including the expression of vimentin/CD99/cytokeratins/α-smooth muscle actin and vimentin/CD99/S-100 protein in case 1 and case 2, respectively, suggested the possibility of Ewing sarcoma (EWS)/PNET. However, molecular analyses failed to show the presence of the EWS/FLI-1 and EWS/ERG fusion transcripts, indicative of the most common translocations, i.e., t(11;22)(q24;q12) and t(22;21)(q22;q12), occurring in this tumor family. The revision of both cases included an immunohistochemical analysis with a commercially available anti-INI1 protein antibody. Immunohistochemistry, showing the absence of INI1 expression in neoplastic cells, strongly supported the diagnosis of MRT. Ultrastructural studies, performed on formalin-fixed tissues, were consistent with the diagnosis of MRT. This study suggests including anti-INI1 protein antibody in the immunohistochemical panel when evaluating pediatric tumors with ambiguous morphological and immunohistochemical features, particularly from small biopsies. A careful evaluation of clinical, pathological, and molecular findings is the key to a correct diagnostic approach of pediatric tumors.

Original languageEnglish
Pages (from-to)451-457
Number of pages7
JournalPathology Research and Practice
Issue number7
Publication statusPublished - Jul 15 2009



  • INI1 protein
  • Pediatric
  • Rhabdoid tumor
  • Unusual morphology

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Cell Biology

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