3.O.11 EXTRATHORACIC SOLITARY FIBROUS TUMOUR: A RARE ENTITY WITH AN UNPREDICTABLE BEHAVIOUR

Abstract

Solitary fibrous tumour (SFT) is a relatively uncommon mesenchymal neoplasm that most frequently arises in the pleura, but is also known to affect extrathoracic sites. About 15 % of SFT’s behave in an aggressive way, giving rise to local recurrence and/or distant metastasis. However, the behaviour of SFT remains unpredictable and due to the rarity of this tumour, it is difficult to define prognostic factors. The purpose of this study was to describe our experience with SFT, trying to define the pathologic features of this rare entity and better understand its clinical behaviour.

We performed a clinicopathologic review of all cases treated for a SFT at the Istituto Ortopedico Rizzoli in Bologna, between 1996 and 2008. We included 24 patients, nine males and fifteen females, ranging in age from 22 to 82 years (median 43.5 years). The anatomical sites involved were: the thigh (12 cases), shoulder region (four cases), gluteus (three cases), foot (two cases), extrapleural thoracic wall (two cases), and the lower leg (one case).

The tumour was > 5 cm in 15 cases, ranging in diameter from 2.5 cm to 18 cm (median 7.5 cm). Pain and swelling were the most frequently reported symptoms at presentation, with a mean duration of symptoms of 10 months. All patients were treated by excisional surgery (wide margins in 11, marginal margins in 13). Three patients had undergone pre-operative radiotherapy (44Gy) and one of these had also adjuvant radiotherapy after marginal excision of the tumour. Six tumours showed at least one atypical histologic feature (moderate to marked cytological atypia, extensive tumor necrosis, ≥ four mitoses per ten high-power fields, or infiltrative margins). On immunohistochemistry, 21 cases were positive for CD-34, 10 for CD-99, 17 for vimentin, three for CD-31, four for actin and one for S-100. Subsequent follow-up (average 33 months, range 5 to 112 months) revealed tumour relapse in only one case: a bone metastasis after 36 months of follow-up. The initial lesion was considered a large, deep, malignant SFT of the thigh, treated with wide surgical excision.

In the current review, including 24 extrathoracic solitary fibrous tumours, all lesions but one had a benign course. Nevertheless, this entity has a potential to recur or metastasize, and therefore careful long-term follow-up is necessary for all patients, even after wide excisional surgery. Although specific prognostic factors are yet to be defined, a high degree of suspicion for malignant behaviour is warranted for those cases in which atypical histologic features are present, particularly in the context of a deep tumor > 5cm in diameter.