College of American Pathologists

2010 — September Case of the Month

Posted October 06, 2010


CAP Foundation September 2010 Online Case of the Month

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A 19-year-old Caucasian man presented with a rapidly growing, painful, firm mass of the left buttock. Imaging revealed a heterogeneously enhancing 8.0 cm mass in the sacrococcygeal area without bony involvement. An excisional biopsy revealed an ill-defined heterogeneous mass with a grey-tan, somewhat friable cut surface, and gross areas of hemorrhage and necrosis. Immunohistochemistry showed strong membranous staining for CD99, with negative reactivity for multiple cytokeratins, CD45, desmin, smooth muscle actin, S100 protein, synaptophysin, chromogranin, and MyoD-1. Fluorescence in-situ hybridization performed on touch preparations of the tumor showed the presence of a t(11;22) translocation in all examined tumor cells.

The master list with the correct answer

  • Alveolar rhabdomyosarcoma
  • Desmoplastic small round cell tumor
  • Ewing sarcoma/Primitive neuroectodermal tumor
  • Lymphoblastic lymphoma
  • Metastatic small cell carcinoma
  • Neuroblastoma

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  • Appropriate diagnosis
  • Critique
  • References

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