[59] Heterotopic Bone in Epithelioid Sarcomas: A Histopathological Review of 4 Cases

SA Koplin, GP Nielsen, AE Rosenberg. Massachusetts General Hospital, Boston, MA

Background: Epithelioid sarcoma is an uncommon malignancy which usually arises in the superficial soft tissues of the extremities. Classically, epithelioid sarcomas grow as nodules of moderately atypical epithelioid cells with central necrosis. The stroma is variably fibrous and rarely may contain heterotopic bone. The presence of bone within epithelioid sarcoma has received little attention in the literature.
Design: We reviewed our surgical pathology files from 1987 to 2008 and identified 91 cases of epithelioid sarcoma. Four tumors contained heterotopic bone and they formed the study group. Histologic sections from these four cases were reviewed, and the heterotopic bone was characterized by location (peripheral versus central), architecture (woven versus lamellar) and type (cancellous versus cortical-like). We also noted the presence or absence of prominent osteoblastic rimming, cartilage and mineralization.
Results: The results are summarized Table 1. The diagnosis of epithelioid sarcoma was confirmed by morphology, immunohistochemistry and ultrastructural analysis, when available. Analysis of the heterotopic bone revealed predominantly woven bone which was located both centrally and peripherally. The majority of the woven bone was trabecular in architecture, but cortical-like bone was identified as well as small foci of mature lamellar bone. Osteoblastic rimming was variable and ranged from minimal to prominent. The bone was generally mineralized and small foci of cartilage with enchondral ossification were present in two of the tumors.

Patient Data

Patient	Age	Location	Size (cm)	Location of Bone	Architecture of Bone	Type of Bone	Osteoblastic Rimming
1	40	Forearm	11	Peripheral and central	Woven	Trabecular	Prominent
2	5	Base of Skull	Unknown	Peripheral and central	Woven, focal lamellar	Trabecular	Minimal to focally prominent
3	45	Forearm	4.5	Predominantly peripheral, focal central	Woven, focal lamellar	Trabecular, focal cortical-like	Minimal
4	27	Forearm	11	Peripheral and central	Woven, focal lamellar	Trabecular	Minimal

Conclusions: Epithelioid sarcomas infrequently contain heterotopic bone. When present, the bone may be located throughout the mass, is largely woven in architecture and trabecular in configuration, is often rimmed by osteoblasts and is mineralized. The presence of heterotopic bone raises a broad differential diagnosis including both non-neoplastic, reactive tumors such as myositis ossificans as well as benign and malignant neoplasms including ossifying fibromyxoid tumor, synovial sarcoma and osteosarcoma.
Category: Bone & Soft Tissue

Monday, March 9, 2009 1:00 PM

Poster Session II # 26, Monday Afternoon