Adult-type Fibrosarcoma: A Reevaluation of 163 Putative Cases Diagnosed at a Single Institution Over a 48-year Period

Adult-type fibrosarcoma (FS) was once considered the most common adult sarcoma, but is now considered a diagnosis of exclusion. No recent series has critically reevaluated putative FSs to estimate their true incidence. One hundred ninety-five cases diagnosed as adult FS in somatic soft tissue were retrieved from our institutional archives for the period 1960 to 2008. Thirty-two cases with insufficient material were excluded. On the basis the morphology of the final 163 cases, immunohistochemical studies (IHC) was conducted using some combination of: wide-spectrum cytokeratin (CK), EMA, high molecular weight CK, S100, Melan A, HMB-45, CD34, TLE1, CD31, HHV8, smooth muscle actin, desmin, ALK1, CD99, Myo-D1, myogenin, c-kit, INI1, CD21, p63, calretinin, WT1, and TTF1. Fluorescence in situ hybridization analysis for SYT gene rearrangement was done in 6 putative CK-negative synovial sarcomas (SS). Revised diagnoses were based on clinical, morphologic, IHC, and molecular findings. The original group of putative FS occurred in 84 males and 79 females (median 52.5 y, range 2 to 99 y), and involved various anatomic sites. Only 26 cases met WHO criteria for FS, including 2 postradiation FS. These occurred in 16 males and 10 females (median 50 y, range 6 to 74 y), and involved the lower extremities (12 cases), head/ neck (5 cases), trunk (4 cases), upper extremities (3 case), and mediastinum/abdomen (2 cases). Clinical follow-up information was available for 24 of 26 (92%) cases, with a median of 5 years follow-up (range <1 to 35 y). Twelve patients (50%) died of locally aggressive and/or metastatic disease (median follow-up 1-year; range <1 to 8 y), 6 patients (25%) were alive without disease (median follow-up 11.5 y; range 2.5 to 35 y), and 6 patients (25%) died of other causes (median follow-up 10 y; range 9 to 18 y) (). Fluorescence in situ hybridization analysis was positive for SYT gene rearrangement in all cases tested. Non-FS (137 cases) were reclassified as: undifferentiated pleomorphic sarcoma (32 cases), SS (21 cases), solitary fibrous tumor (14 cases), myxofibrosarcoma (11 cases), malignant peripheral nerve sheath tumor (8 cases), FS dermatofibrosarcoma protuberans, and desmoplastic melanoma (4 cases each), low-grade fibromyxoid sarcoma, sarcomatoid carcinoma, desmoid-type fibromatosis, rhabdomyosarcoma, myofibroblastic sarcoma, spindle-cell liposarcoma (3 cases each), sclerosing epithelioid FS, fibroma-like epithelioid sarcoma, leiomyosarcoma, cellular fibrous histiocytoma (2 cases each), and others (17 cases). Using modern diagnostic criteria with ancillary IHC and molecular genetics, we have been able to reclassify 84% of putative FS. Exclusive of undifferentiated pleomorphic sarcoma, the distinction of which from FS is subjective, 64% of putative FS were reclassified, most commonly as monophasic SS and solitary fibrous tumor. We conclude that true FS is exceedingly rare, accounting for <1% of approximately 10,000 adult soft tissue sarcomas seen at our institution during this time period, and should be diagnosed with great caution.