Discussion

Klemperer and Rabin first described SFTs in 1931. These are soft-tissue spindle-cell neoplasms. SFTs are classified by the World Health Organization (WHO) as intermediate fibroblastic or myofibroblastic tumours, which means that SFTs are considered tumours that rarely metastasize. These tumours usually affect the pleura. 30% of these tumours are reported to be extra-pleural which includes the salivary glands, nasal cavity, orbit, the upper respiratory tract, thyroid, genitourinary system, peritoneum, retroperitoneum and pelvis.
As the case described above, SFTs in the retroperitoneum, are rarely found and less than 100 cases have been described so far. The main features of SFTs are the large size they can reach as they do not have any specific symptoms. This leads to the need for major surgery for resections of the primary.
The tumour on microscopic examination has a “patternless pattern” which makes histopathological diagnosis challenging. This pattern is a storiform arrangement of spindle cells combined with a “hemangiopericytoma-like appearance” and increased vascularity of the lesion. Other spindle cell tumours such as leiomyoma, angiomyolipoma, inflammatory myofibroblastic tumours, and gastrointestinal stromal tumours are some of the differential diagnoses.
Immunohistochemistry is very helpful. Solitary Fibrous Tumours are positive for Bcl-2, vimentin, CD99, and CD34 and negative for expression of S100, cytokeratin, EMA, SMA, CD117, CD31, and desmin normally. Around 75% of extrapleural SFTs express a positive for a combination of Bcl-2 and CD34, which guides histopathologically towards the diagnosis of SFT.
If SFTs show high mitotic activity (that is more than 4 mitoses in 10 HPF), high cellularity, necrosis, pleomorphism and hemorrhagic activity in histopathological examination, they are considered to be malignant.
Sometimes, paraneoplastic syndromes may be present in SFTs, mainly hypoglycemia. It is thought to arise due to tumour producing Insulin-like growth factor – 2 (IGF-2). These paraneoplastic symptoms may sometimes be the presenting symptoms for these tumours. Normally when complete resection is achieved by surgery, these symptoms subside.
Computed Tomography imaging is unable to differentiate primary retroperitoneal SFTs from other solid retroperitoneal tumours; however, for the surgeons, it is invaluable as it gives an anatomical overview and provides information required to plan the right approach and strategy for complete resection of the tumour with clear margins.
Surgery is the mainstay of treatment and the only effective treatment available in most cases. When there is a clear negative margin, the recurrence rates appear to be low and positive resection margins affect the recurrence rates.
As SFTs are quite rare, especially more so in retroperitoneum, there is a lack of studies that define the best management guidelines. For adjuvant treatment, only case reports and observational studies are available which are also dependent upon individual cases. The tumour has high vascularity therefore, antiangiogenic drugs, such as bevacizumab, interestingly, are used initially. An important study on the matter proposed a strategy to use conventional chemotherapeutic agents to keep the disease stable and for treating advanced disease. Local and distant recurrences and distant seen even in benign cases, which show unpredictable behaviour, with the potential for malignant transformation.
The potential of SFT for malignant transformation is the basis of performing computed tomography during follow-up.