[98] Haemangiopericytoma of Bone: Real or Imagined?

SL Verbeke, CD Fletcher, P Picci, S Daugaard, HM Kroon, PC Hogendoorn, JV Bovee. Leiden University Medical Center, Leiden, Netherlands; Brigham and Women's Hospital, Boston; Rizzoli Institute, Bologna, Italy; Rigshospitalet, Copenhagen, Denmark

Background: Haemangiopericytoma (HPC) was first described by Murray and Stout as a soft tissue neoplasm with distinct morphologic features, presumably composed of pericytes. Over the years, it became clear that many tumors could mimic a HPC-like pattern. These days, it is accepted that in soft tissue most lesions diagnosed as HPC in the past are actually solitary fibrous tumors (SFT), synovial sarcomas (SS) or myofibromatoses. It has been unclear whether the very rare HPC of bone is a true entity, or that the HPC-like vessels are non-specific and part of other, different entities.
Design: We collected 10 primary HPC of bone from 4 institutions diagnosed between 1952 and 2002. All clinical, radiologic and pathologic data were reviewed. Immunohistochemistry was performed for CD31, CD34, factor VIII, SMA, keratin AE1/AE3 and EMA.
Results: There were 5 female and 5 male patients between 21 and 73 years of age (mean 45.3). All tumors were located within bone. The primary site of the tumor was the femur in two patients, humerus in one, fibula in one, sacrum in two and vertebra in three. All tumors showed the presence of prominent thin-walled branching vessels surrounded by more undifferentiated spindle or round cells. However these cells showed some variation in their morphologic pattern: 5 tumors showed a patternless architecture and varying cellularity, consistent with SFT. Three tumors showed more densely packed sheets of poorly differentiated cells, similar to SS, and 1 case each represented paraganglioma and PEComa, possibly metastatic. Tumors resembling SFT showed usually focal to diffuse staining for CD34. All tumors were negative for SMA. Two tumors more similar to SS showed focal positive staining for keratin AE1/AE3 or EMA (66%). Some tumors showed severe decalcification artefact. None of the 10 tumors show CD31 and factor VIII expression. FISH is performed to study SYT rearrangements.
Conclusions: Our retrospective review of tumors diagnosed as HPC of bone in the past revealed the absence of true pericytic differentiation and the existence of both SFT of bone and SS of bone. Therefore, as in soft tissue tumors, HPC-like features are non specific. Diffuse CD34 staining is helpful to diagnose SFT of bone, whereas focal keratin/ EMA staining is suggestive for SS of bone.
Category: Bone & Soft Tissue

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 2, Tuesday Morning