[70] Dedifferentiated Solitary Fibrous Tumors: A Clinicopathologic Study of 7 Cases

RS Macarenco, MR Erickson-Johnson, X Wang, AG Nascimento, AL Folpe, AM Oliveira. CIPAX-Medicina Diagnostica, Sao Jose dos Campos, SP, Brazil; Mayo Clinic, Rochester, MN

Background: Solitary fibrous tumor (SFT) is a fibroblastic neoplasm.Histological features associated with malignant behavior include high cellularity, mitotic activity (>4/10 HPF), nuclear pleomorphism, necrosis, size >5 cm, and infiltrative tumor borders.Clinicopathologic features of dedifferentiated SFT (DD-SFT), defined as high grade undifferentiated sarcoma juxtaposed to a histologically classic SFT, have not been described in detail.
Design: Seven DD-SFT were retrieved from our archives.Histological slides were reviewed; immunohistochemistry and ploidy digital image analysis were performed when possible.Clinical information including treatment and follow-up were added.
Results: Cases occurred in 4M and 3F, with a median age of 64ys (range 49-73 ys).Sites included lung, axilla, thigh, upper back, paratestis, and scalp.Median tumor size was 9 cm (range 4-10 cm).All cases had areas of histologically typical SFT juxtaposed to malignant areas. Six cases had abrupt transition between typical and DD-SFT, whereas in one case the components were intermixed. Dedifferentiated areas comprised 10 to 95% of each case and consisted of pleomorphic sarcoma (5 cases), pleomorphic sarcoma of the inflammatory type (1 case), and undifferentiated sarcoma with an epithelioid and pseudo-alveolar pattern (1 case).Cellularity, nuclear atypia and pleomorphism, and mitotic activity were higher in the DD areas (mean=102/50 HPF) as compared to the more typical areas (mean=48/50HPF).Tumor necrosis and vascular invasion were identified in the DD component of two cases.All cases showed diffuse CD34 expression in areas of typical SFT; DD areas showed uniformly retained (4 cases), partially retained (1 case) and absent (1 case) CD34 expression.All tumors were negative for S100 protein, smooth muscle actin, desmin and cytokeratin. DIA showed aneuploidy in both areas in 4 (of 4) cases evaluated.Outcome (available in 4) showed that 2 patients presented with metastatic disease (1 died 1 month after diagnosis and the other was well 1 month after surgery), 1 patient was alive with local recurrence 3.5 years after diagnosis, and one patient free of disease 2 years after diagnosis.
Conclusions: Dedifferentiation represents a rare form of progression in SFT. Additional cases are necessary to more fully understand their natural history. Follow-up to date suggests behavior more aggressive than conventional malignant SFT, akin to other types of dedifferentiated sarcoma.
Category: Bone & Soft Tissue

Monday, March 9, 2009 11:30 AM

Platform Session: Section E, Monday Morning