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Aquesta Uropathology, Toowong, Qld, AustraliaDepartment of Pathology and Molecular Medicine, Wellington School of Medicine and Health Sciences, University of Otago, Wellington, New ZealandSouthern Community Laboratories, Wellington, New Zealand
Solitary fibrous tumour (SFT) is a fibroblastic neoplasm which can originate in multiple anatomical sites, being most frequently seen in the pleura and soft tissues.
Moch H. Humphrey P.A. Ulbright T.M. Reuter V.E. WHO Classification of Tumours of the Urinary System and Male Genital Organs. 4th ed. IARC Press,
Lyon2016
A 63-year-old female presented with malaise and weight loss and was found on radiological investigation to have two expansile tumours involving the right kidney. She had a past history of a left radical nephrectomy followed by radiation therapy 28 years previously, for a tumour diagnosed as a primary renal haemangiopericytoma. This was described as large (approximately 15 cm in maximum dimension) and highly vascular but confined to the kidney. Five years later she developed a tumour in the thoracic spine, and another 13 years later a tumour in the left lower lobe of the lung, both of which were resected and diagnosed as recurrent haemangiopericytoma. The patient is now 6 months post-operative and is tumour free and on no adjuvant therapy.
The surgical specimens consisted of two partial nephrectomies from the right kidney, one from the anterior mid kidney and the other from the posterior upper pole. Tumour 1, measuring 35 mm in maximum extent, was located largely in the perinephric fat, with a small intrarenal cortical component. The tumour was solid, cream-coloured, lobulated, with a soft, fleshy and homogenous cut surface. Tumour 2 was well circumscribed, measuring 44 mm in maximum extent and involved both the renal cortex and medulla. The cut surface of the tumour was solid and cream-coloured with foci of haemorrhage (Fig. 1A).
Fig. 1(A) Gross specimen of tumour. The tumour is solid and cream-coloured with extensive areas of haemorrhage; (B) solitary fibrous tumour showing hypercellularity and moderate nuclear pleomorphism; (C) focal areas of hypocellularity; (D) prominent vascular channels; (E) interstitial collagenous stroma.
Both tumours were similar histologically, being highly cellular with rare paucicellular foci composed largely of myxoid stroma. Spindled to ovoid cells with scanty to moderate amounts of pale cytoplasm were arranged in sheets with a prominent vascularity, consisting of branching, thin-walled dilated (staghorn) channels. In some areas, dense eosinophilic stromal collagen was seen (Fig. 1B–E). Tumour nuclei were hyperchromatic with moderate pleomorphism. Nucleoli were not prominent. The mitotic count was up to 30 per 10 high power fields. No granular tumour necrosis
was identified. Tumour 1 invaded perinephric fat and tumour 2 invaded perinephric fat and renal sinus blood vessels (Fig. 2A). The morphological features of both tumours were consistent with SFT.
Fig. 2(A) Solitary fibrous tumour with infiltration of the renal sinus; (B) CD99 immunohistochemistry; (C) STAT6 immunohistochemistry; (D) CD34 immunohistochemistry.
The differential diagnosis included synovial sarcoma, sarcomatoid renal cell carcinoma, renal angiosarcoma, Ewing's tumour and rhabdomyosarcoma. Immunohistochemical staining showed strong and diffuse positivity for CD99 and STAT6 confirming the diagnosis of SFT. Areas of strong cytoplasmic positivity for CD34 was also noted (Fig. 2B–D). There was nuclear reactivity for FLI-1, while immunostains for WT1, keratin, desmin, smooth-muscle actin, ERG, S100 protein, synaptophysin, TLE-1 and myogenin were negative. Fluorescence in situ hybridisation (FISH) showed no rearrangement for ETV6 (excluding cellular mesoblastic nephroma) and in EWSR1 (excluding Ewings family tumours). While NAB2-STAT6 gene fusions are pathognomonic for SFT,
the genes are closely located on 12q13 and as such can only rarely be detected by conventional chromosome banding or fluorescence in situ hybridisation but are detected by immunohistochemistry.
Most SFTs display low cellularity and a low mitotic count without substantial pleomorphism or granular tumour necrosis. The risk of local or metastatic recurrence of SFT has been correlated with several clinical and histological features.
These include patient age, tumour site and size, a high mitotic count of >4 mitoses per 10 high power fields, tumour cellularity, granular tumour necrosis and nuclear pleomorphism. Given the high cellularity, nuclear atypia, high mitotic count, involvement of perinephric fat and renal sinus vascular channels, the aggressive behaviour of the tumours in our case is not unexpected.
Tumours previously labelled haemangiopericytoma are unified under the term SFT in the current World Health Organization classification.
The occurrence of two pT3a staging category renal SFTs in a patient with a past history of primary haemangiopericytoma in the contralateral kidney followed by metastatic tumours in the thoracic spine and lung, also reported as haemangiopericytoma, is consistent with the current renal tumours being metastatic SFTs.
Bilateral renal SFTs arising from a renal primary SFT are extremely rare with only two cases being reported in the literature. In one of the cases synchronous tumours were seen in a 51-year-old female who had been diagnosed with tuberous sclerosis and had no other malignancies.
In the other case there was metachronous development of renal SFT. The patient was a 49-year-old female who developed a SFT in the right kidney 8 years after undergoing renal artery embolisation and left radical nephrectomy for a primary renal SFT.
While bilaterality of renal tumours often raises the possibility of a genetic predisposition, this would appear unlikely for these cases. As there is no reported association between SFT and tuberous sclerosis, the occurrence of this in one of the cases appears nothing more than coincidental.
Bilateral renal SFT has also been noted in patients who have developed metastases from an extra-renal SFT primary. To date eight such cases have been reported (Table 1). In seven of these cases, the central nervous system was the primary site, while in the other case the patient had an inguinal primary. The development of renal metastases in these eight cases indicates that in cases where renal SFT is diagnosed, consideration should be given to the probability that there is an extra-renal primary tumour. SFT is known to be associated with late metastases; however, the 28-year survival interval in our case is startling and would suggest that follow-up should be lifelong, especially for cases with an apparently aggressive histology.
Table 1Cases of bilateral metastatic renal solitary fibrous tumour
Moch H. Humphrey P.A. Ulbright T.M. Reuter V.E. WHO Classification of Tumours of the Urinary System and Male Genital Organs. 4th ed. IARC Press,
Lyon2016
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