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Presented by Pedram Argani, M.D. and prepared by Mohammed Lilo, M.D.
Case 1: This is a 7 year old female with thigh mass.
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Question 1 of 1
1. Question
Week 585: Case 1
This is a 7 year old female with thigh massimages/lilo/Arg-1-B.jpg
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images/lilo/Arg-1-E.jpgCorrect
Answer: Alveolar rhabdomyosarcoma
Histology: This is a small round blue cell tumor. The tumor has solid architecture in many areas, but in other areas these cells are discohesive and cling to fibrovascular septa, giving an alveolar architecture. The cells have dark, angulated nuclei, and focally eccentric dense eosinophilic cytoplasm. The lesional cells demonstrated diffuse immunoreactivity for myogenin and desmin, supporting the diagnosis of alveolar rhabdomyosarcoma. By RT-PCR, the lesion demonstrated a characteristic PAX3- FKHR gene fusion.
Discussion: Embryonal rhabdomyosarcoma is essentially spindle cell lesion. Densely cellular areas of embryonal rhabdomyosarcoma can mimic alveolar rhabdomyosarcoma, but these lesions should demonstrate less diffuse labeling myogenin and have spindling elsewhere. Intra-abdominal desmoplastic small round cell tumor would also label for desmin, but typically features more desmoplastic stroma and lacks myogenin immunoreactivity. Ewing sarcoma may occasionally label for desmin, but should not label for myogenin and has a characteristic EWS-FLI1 gene fusion.
Incorrect
Answer: Alveolar rhabdomyosarcoma
Histology: This is a small round blue cell tumor. The tumor has solid architecture in many areas, but in other areas these cells are discohesive and cling to fibrovascular septa, giving an alveolar architecture. The cells have dark, angulated nuclei, and focally eccentric dense eosinophilic cytoplasm. The lesional cells demonstrated diffuse immunoreactivity for myogenin and desmin, supporting the diagnosis of alveolar rhabdomyosarcoma. By RT-PCR, the lesion demonstrated a characteristic PAX3- FKHR gene fusion.
Discussion: Embryonal rhabdomyosarcoma is essentially spindle cell lesion. Densely cellular areas of embryonal rhabdomyosarcoma can mimic alveolar rhabdomyosarcoma, but these lesions should demonstrate less diffuse labeling myogenin and have spindling elsewhere. Intra-abdominal desmoplastic small round cell tumor would also label for desmin, but typically features more desmoplastic stroma and lacks myogenin immunoreactivity. Ewing sarcoma may occasionally label for desmin, but should not label for myogenin and has a characteristic EWS-FLI1 gene fusion.
