SFT represents a distinct entity within the wide range of soft tissue tumors. Its cellular origin is believed to be fibroblastic in type. Most cases of formerly diagnosed "hemangiopericytomas" seemingly share essential features with SFT and may indeed represent true SFT. According to overlapping histological criteria between SFT and hemangiopericytoma, SFT represents a wider range of neoplasias (probably in fact including the former "favourite" diagnosis of hemangiopericytoma) which should best be regarded as a "waste basket" and be considered a mere diagnosis of exclusion. The lipomatous variant of SFT ("lipomatous hemangiopericytoma") includes a mature fat component intermingling with typical areas of SFT. Rare myxoid SFT may cause considerable problems in differential diagnosis to more aggressive soft tissue neoplasms or soft tissue tumors of another differentiation. Branching and ectatic blood vessels typical for SFT known as hemangiopericytoma-like vessels may be a feature of several other predominantly malignant soft tissue tumors (e.g. synovial sarcomas or malignant peripheral nerve sheath tumors), implicating that a wider range of other soft tissue neoplasias has to be considered in the histopathological differential diagnosis of SFT. The so-called "patternless pattern" or the combination of different histological patterns such as storiform, fascicular, neuraltype, diffuse sclerosing, and heringbone growth pattern may lead to a wrong diagnosis [19
]. Therefore, it is evident that an experienced soft tissue pathologist should evaluate the specimens. For differential diagnosis, so-called hemangiopericytoma, synovial sarcoma, dermatofibrosarcoma protuberans, leiomyosarcoma, malignant peripheral nerve sheath tumor, and liposarcoma, should be taken into consideration. Positron emission tomography (PET) may be helpful to distinguish between a malignant and a benign variant of the tumor [20
], but the gold standard for diagnosis remains incisional biopsy.
Extrathoracic solitary fibrous tumors (ESFT) by now have been reported at almost every anatomic location, but reports of tumors at the extremities or intramuscular tumors as well as tumors with malignant clinical behaviour or atypical histologic features are rare [1
Other series of ESFT's showed almost equal distribution of the incidence for male and female, with patients' ages ranging from the third to the eighth or ninth decade with a maximum in the sixth decade concurring with our data [3
Some studies suggested a very low rate of recurrence and metastasis [8
], whereas other authors indicated a possibly increased relapse rate with extended follow-up periods. In their studies Vallat-Decouveleare et al. and Gold et al. [3
] in their studies found local recurrence in 4.3% and 6.7% and metastasis in 5.4% and 5.3%, respectively. Tumor relapse occurred after up to 168 months, but most of the metastasis or local recurrences were diagnosed within the first two years after initial treatment. Sites of distant metastasis were lung, liver, bones, mesentery, omentum, mediastinum and retroperitoneum with preference for lung and liver [1
Vallat-Decouveleare suggested atypical histologic features, such as nuclear atypia, areas of increased cellularity, necrosis and 4 or more mitoses per 10 HPF as being predictive for clinical malignant behaviour of the tumor and found local or distant relapse in those cases in 80%, but also reported a case of clinically malignant behaviour of a histological benign appearing case. Recurrent tumor specimens showed a higher grade of atypia than the primary tumor but usually retained their immunohistochemical profile. Gold's data proposed to add the size of the primary tumor as well as the resection status to the predictive factors of clinical behaviour. Positive surgical resection margins and primary tumor sizes of more than 10 cm were positively correlated with unfavourable clinical outcome.
In our series, the only patient with recurrent disease and metastasis was primarily resected incompletely, underlining this suggestion. In the recurrent tumor specimen increased atypia was seen, but if this atypia had already been present in the primary tumor and therefore could be considered as of predictive value cannot be determined. The recurrence occurred 2 years and the metastasis 2 ½ years after primary resection and following radiation. Detailed histopathological information about the primary tumor could not be obtained.
Complete surgical resection is commonly accepted as treatment of choice for ESFT. Due to improved techniques in reconstructive surgery, even large lesions can usually be completely resected, preserving the limbs. Amputations should be limited to extended or recurrent tumors. Befitting the rareness of this entity reports of radiation therapy and chemotherapy of ESFT are anecdotal and so far, no significant benefit of adjuvant treatment has been reported. In some cases, especially malignant variants or incomplete resections with no further surgical option, it may although be used [1
]. This concurs with the findings for intrathoracic SFT [24
According to the late recurrence or metastasis, long follow-up periods (at least 15 years) should be maintained with closer follow-up during the first two years. In cooperative patients a life long follow-up may be recommended. Follow-up should include clinical examination as well as abdominal ultrasound and chest x-ray.