[25] Primary Fibrosarcoma of Bone (PFSB): A Re-Evaluation of Cases Seen at a Single Institution for the Period 1913 – 2009

Faye L Chang, Andrew L Folpe, Carrie Y Inwards. Mayo Clinic, Rochester, MN

Background: PFSB, currently defined by the WHO as a “primary malignant spindle cell neoplasm of bone in which the tumor cells are typically organized in a fascicular or 'herringbone' pattern", is thought to account for <5% of primary bone tumors. However, its true incidence is difficult to discern, owing to changes in diagnostic terminology over time and improved recognition of fibrosarcoma (FS) mimics with modern ancillary techniques. We re-evaluated a large series of tumors previously diagnosed as FS involving bone in order to more precisely define criteria for the diagnosis of PFSB in the modern era, and to better elucidate the incidence of such tumors.
Design: All available slides from 161 cases diagnosed as PFSB involving bone for the period 1913 -2009 were retrieved from our archives. Clinical records, pathology and radiology reports were reviewed. Secondary FSs, cases without adequate slides, and FSs secondarily involving bone were excluded, leaving a study population of 97 cases. Criteria for diagnosis included: 1) spindle cell morphology and a fascicular growth pattern, 2) no more than moderate pleomorphism, 3) absent osteoid production, and 4) absent expression by immunohistochemistry (IHC) of other than limited smooth muscle actin (SMA). IHC for cytokeratins (OSCAR and AE1/AE3), SMA, desmin, S-100, and CD34 was performed using commercial antibodies and the Dako Envision detection system. IHC for TLE-1 failed due to specimen decalcification.
Results: Of the remaining 97 study cases, 64 were considered not to meet morphological criteria for PFSB. These were predominately reclassified as pleomorphic sarcomas. This left a study group of 33 cases. Of these, 15 were reclassified as leiomyosarcoma, 7 as probable synovial sarcoma, and 1 as myoepithelioma. 10 cases met our criteria for PFSB; these occurred in 6 F and 4 M (age range 6 to 76 yrs) and involved the femur (3), sacrum (2), and 1 each in the fibula, humerus, tibia, pubis, and scapula.
Conclusions: Using strict diagnostic criteria and ancillary IHC, we found PFSB to be extremely rare, accounting for <1% of primary bone sarcomas seen at our institution. PFSB should be distinguished from its many potential mimics, most commonly leiomyosarcoma and synovial sarcoma. The natural history of PFSB remains to be fully established, particularly as prior series of such tumors have likely included what we would now consider to represent non-PFSB. On-going molecular genetic studies should help to more clearly establish the incidence of reclassified osseous synovial sarcoma.
Category: Bone & Soft Tissue

Tuesday, March 20, 2012 11:15 AM

Platform Session: Section G, Tuesday Morning


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