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.