Pediatric extra-renal rhabdoid tumors with unusual morphology: a diagnostic pitfall for small biopsies.
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.
Alaggio
Rita
R
Dipartimento di Scienze Chirurgiche e Oncologiche, Sezione Anatomia Patologica, Università di Padova, Padova, Italy.
Boldrini
Renata
R
Di  Venosa
Benedetta
B
Rosolen
Angelo
A
Bisogno
Gianni
G
Magro
Gaetano
G
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
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