title: Pediatric extra-renal rhabdoid tumors with unusual morphology: a diagnostic pitfall for small biopsies.
abstract: 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/alpha-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.
authors.affiliation: Dipartimento di Scienze Chirurgiche e Oncologiche, Sezione Anatomia Patologica, Università di Padova, Padova, Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Alaggio
authors.forename: Renata
authors.initials: R
authors.lastname: Boldrini
authors.forename: Benedetta
authors.initials: B
authors.lastname: Di  Venosa
authors.forename: Angelo
authors.initials: A
authors.lastname: Rosolen
authors.forename: Gianni
authors.initials: G
authors.lastname: Bisogno
authors.forename: Gaetano
authors.initials: G
authors.lastname: Magro
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis* / Q000235:genetics; D001706:Biopsy; D017024:Chemotherapy, Adjuvant; D002675:Child, Preschool; D002868:Chromosomal Proteins, Non-Histone / Q000032:analysis*; D004268:DNA-Binding Proteins / Q000032:analysis*; D003951:Diagnostic Errors / Q000517:prevention & control*; D017809:Fatal Outcome; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D007223:Infant; D008854:Microscopy, Electron; D015514:Oncogene Proteins, Fusion / Q000235:genetics; D011237:Predictive Value of Tests; D051789:Proto-Oncogene Protein c-fli-1 / Q000235:genetics; D034802:RNA-Binding Protein EWS; D018714:Radiotherapy, Adjuvant; D012186:Retroperitoneal Neoplasms / Q000737:chemistry / Q000235:genetics / Q000473:pathology* / Q000628:therapy; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018335:Rhabdoid Tumor / Q000737:chemistry / Q000235:genetics / Q000473:pathology* / Q000628:therapy; D000071796:SMARCB1 Protein; D012512:Sarcoma, Ewing / Q000737:chemistry / Q000235:genetics / Q000473:pathology* / Q000628:therapy; D013125:Spinal Neoplasms / Q000737:chemistry / Q000235:genetics / Q000473:pathology* / Q000628:therapy; D014157:Transcription Factors / Q000032:analysis* / Q000235:genetics
chemical_list: D014408:Biomarkers, Tumor; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; C450460:EWS-ERG fusion protein, human; C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D000071796:SMARCB1 Protein; C513266:SMARCB1 protein, human; D014157:Transcription Factors