Solitary fibrous tumour is the most common benign mesenchymal pleural neoplasm and was first described by Klemperer & Rabin as a form of localized fibrous mesothelioma. 

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Subsequent ultrastructural studies revealed that the tumour cells did not have features of mesothelial cells and showed fibroblastic features.

It is now believed that the tumour is derived from the sub-mesothelial connective tissue, and not from mesothelial cells. There is no association with exposure to asbestos.

These tumours, which may achieve immense size, usually arise from the visceral pleura from a narrow pedicle and may fill the hemithorax .

Less commonly, they take origin from the parietal layer or a fissure so that they project into the lung parenchyma.

They have now been described in many sites throughout the body.

Remarkably, up to half of patients are asymptomatic at presentation, the tumour being an incidental finding on chest X-ray. Symptoms of chest pain, dyspnea and fever have been reported. Others have insidious respiratory symptoms, clubbing and hypertrophic osteoarthropathy.

The histological appearance are variable - cellular with storiform or pericytomatous foci, myxoid, fibrous or sclerotic.  Image Link

It is not surprising, therefore, that these tumours have been termed fibromas, leiomyomas, fibrous histiocytomas, nerve sheath tumours, fibrous mesotheliomas etc.  Visit: Soft Tissue Pathology;

The two basic elements present in varying proportions: (i) a solid spindle cell component and (ii) a diffuse sclerosing component.

A highly distinctive appearance of these tumours is the deposition of rope-like strands of keloidal collagen in parallel distribution alongside the spindle cells.

The majority are indolent, but 10-15% are more aggressive with a tendency to infiltrate locally and recur. A high mitotic rate, extensive haemorrhage and necrosis portend a less favourable outcome.

The tumour cells are uniformly positive for vimentin, but are negative for keratin, EMA, actin, desmin, and S-100 protein. CD34 positivity is a useful marker but may be absent in the more malignant examples. Bcl-2 was found to be uniformly and strongly positive in the tumour cells.

Benign solitary fibrous tumour is most often a benign neoplasm which is cured by local excision alone. It has a high cure rate and an 8% local recurrence rate that is usually amenable to curative re-excision.

Malignant solitary fibrous tumour of the pleura (SFTP) ,especially the more common sessile type, has a 63% recurrence rate even with complete resection. The majority of patients with recurrent disease die of the tumor within 2 years. Nevertheless, the overall long-term cure rate for all patients is 88% to 92%.

Clinical and pathological characteristics, such as malignant histology, sessile morphology, and a lower expression of progesterone receptors identify SFTP with a higher risk of recurrence after surgery, and which thus require strict follow-up.

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