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Presented by Pedram Argani, M.D. and prepared by Ali Ansari-Lari, M.D.,Ph.D.
Case 6: An 8-year old male with a thigh mass.
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1. Question
Week 114: Case 6
An 8-year old male with a thigh mass./images/arg6a.JPG
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/images/arg6e.JPGCorrect
Answer: Alveolar soft part sarcoma
Histology: The tumor has an alveolar architecture; that is, it has an arcade-like sinusoidal vasculature which supports discohesive, polygonal tumor cells. The tumor cells have voluminous pink cytoplasm which is well-demarcated by cell membranes, and nuclei with vesicular chromatin and prominent nucleoli. Immunohistochemically, the tumor is negative for all conventional markers with the exception of focal desmin labeling. On PAS diastase stain, rare rod shaped, crystalline cytoplasmic inclusions are identified, which establishes the diagnosis.
Discussion: The compact areas of an alveolar soft part sarcoma can mimic granular cell tumor, particularly in the pediatric age group. The negative labeling for S100 protein in the current case helps eliminate granular cell tumor. An alveolar rhabdomyosarcoma would be more diffusely immunoreactive for desmin, and would label for myogenin, which the current tumor did not. Paraganglioma should show neural differentiation with an S100 positive population of sustentacular cells. Neither was seen in the current case.
Alveolar soft part sarcoma is a rare soft tissue sarcoma of uncertain histogenesis. This tumor typically presents as a painless, slowly growing, soft tissue mass in young adults; however, paradoxically, metastases to lung and brain have often already occurred at presentation. Ultrastructurally, the PAS-positive, diastase resistant rod shaped inclusions correlate with membrane bound crystals with a lattice pattern of fibrils having a diameter of 4 nm and a periodicity of 10 nm. These are associated with the prominent Golgi apparatus, which is thought to give rise to membrane bound granules, which are though to be the precursors of these crystals. In the past year or so, a specific chromosome translocation, derX t(X;17)(p11.2;q25) has been found to be characteristic of alveolar soft part sarcoma. This results in fusion of the TFE3 gene on Xp11.2 to a novel gene, ASPL, on 17q25. Recently, it has been demonstrated that nuclear labeling for the TFE3 protein constitutes a sensitive and specific marker for alveolar soft part sarcoma, and a group of pediatric renal carcinomas, which also bear TFE3 gene fusions. It is likely that this immunostain will become the diagnostic marker of choice for alveolar soft part sarcoma.
Incorrect
Answer: Alveolar soft part sarcoma
Histology: The tumor has an alveolar architecture; that is, it has an arcade-like sinusoidal vasculature which supports discohesive, polygonal tumor cells. The tumor cells have voluminous pink cytoplasm which is well-demarcated by cell membranes, and nuclei with vesicular chromatin and prominent nucleoli. Immunohistochemically, the tumor is negative for all conventional markers with the exception of focal desmin labeling. On PAS diastase stain, rare rod shaped, crystalline cytoplasmic inclusions are identified, which establishes the diagnosis.
Discussion: The compact areas of an alveolar soft part sarcoma can mimic granular cell tumor, particularly in the pediatric age group. The negative labeling for S100 protein in the current case helps eliminate granular cell tumor. An alveolar rhabdomyosarcoma would be more diffusely immunoreactive for desmin, and would label for myogenin, which the current tumor did not. Paraganglioma should show neural differentiation with an S100 positive population of sustentacular cells. Neither was seen in the current case.
Alveolar soft part sarcoma is a rare soft tissue sarcoma of uncertain histogenesis. This tumor typically presents as a painless, slowly growing, soft tissue mass in young adults; however, paradoxically, metastases to lung and brain have often already occurred at presentation. Ultrastructurally, the PAS-positive, diastase resistant rod shaped inclusions correlate with membrane bound crystals with a lattice pattern of fibrils having a diameter of 4 nm and a periodicity of 10 nm. These are associated with the prominent Golgi apparatus, which is thought to give rise to membrane bound granules, which are though to be the precursors of these crystals. In the past year or so, a specific chromosome translocation, derX t(X;17)(p11.2;q25) has been found to be characteristic of alveolar soft part sarcoma. This results in fusion of the TFE3 gene on Xp11.2 to a novel gene, ASPL, on 17q25. Recently, it has been demonstrated that nuclear labeling for the TFE3 protein constitutes a sensitive and specific marker for alveolar soft part sarcoma, and a group of pediatric renal carcinomas, which also bear TFE3 gene fusions. It is likely that this immunostain will become the diagnostic marker of choice for alveolar soft part sarcoma.
