CASE 1. Ewing’s Sarcoma of the Rectum

J. Vardy, A.M. Joshua, S.J. Clarke

Department of Medical Oncology, Sydney Cancer Centre, Royal Prince Alfred Hospital, Sydney, Australia

P.M. Yarrow, B.P.C. Lin

Department of Anatomical Pathology, Concord Repatriation General Hospital, Sydney, Australia

A previously healthy 53-year-old male house painter of Greek origin presented to his local doctor after a single episode of bright rectal bleeding. Additional questioning determined that he had experienced a sensation of heaviness in the rectum for several months. Sigmoidoscopy revealed a fungating, ulcerated posterior wall rectal mass. Treatment necessitated a low anterior resection with formation of a temporary ileostomy. The tumor extended through the full thickness of the rectal wall and to within 7 mm of the resection margin. Histopathology showed an undifferentiated small round blue cell tumor with high mitotic rate and extensive areas of necrosis . Immunoperoxidase stains were positive for MIC-2  and vimentin. There was focal keratin positivity with CAM 5.2. Stains for keratin AE1/AE3, S-100, chromogranin, desmin, and smooth muscle actin were negative. Neuron-specific enolase staining was nonspecific. The tumor cells contained abundant glycogen demonstrated by the periodic acid Schiff stain before and after diastase treatment. No rosette formation was seen. The histologic appearance and immunoperoxidase profile supported a diagnosis of extraosseous Ewing’s sarcoma (EOE). Additional staging using blood results; computed tomography of chest, abdomen, and pelvis; and a whole-body bone scan showed no evidence of disseminated malignancy.

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