|Year : 2015 | Volume
| Issue : 3 | Page : 662
A solitary fibrous tumor of the kidney
Anuruddha M Abeygunasekera1, Anusha P Ginige2, Indika S. H. Liyanage2, Kalana Hareendra1
1 Department of Urology, Colombo South Teaching Hospital, Colombo, Sri Lanka
2 Department of Pathology, Colombo South Teaching Hospital, Colombo, Sri Lanka
|Date of Web Publication||9-Oct-2015|
Anuruddha M Abeygunasekera
Department of Urology, Colombo South Teaching Hospital, Colombo
Source of Support: None, Conflict of Interest: None
A solitary fibrous tumor (SFT) is an uncommon spindle cell neoplasm that usually occurs in the pleura, but may occur in extrapleural sites. Its occurrence in the kidney is rare. We report a SFT, clinically thought to be a renal cell carcinoma arising in the kidney of a 68-year-old female. The tumor was well-circumscribed and composed of a mixture of spindle cells and dense collagenous bands. Immunohistochemical studies revealed reactivity for CD34, CD99, and Bcl-2 protein, with no staining for keratin or muscle markers, confirming the diagnosis. The immunohistochemical study was the key to diagnosis. Several younger members of her family had colorectal and lung cancers suggesting the possibility of a familial or genetic susceptibility.
Keywords: Immunohistochemical study, kidney, solitary fibrous tumor, spindle cells
|How to cite this article:|
Abeygunasekera AM, Ginige AP, Liyanage IS, Hareendra K. A solitary fibrous tumor of the kidney. J Can Res Ther 2015;11:662
| > Introduction|| |
A solitary fibrous tumor (SFT) is an unusual spindle cell mesenchymal neoplasm that usually occurs in the pleura, but has recently been described in diverse extra pleural sites. Its occurrence in the organs of the genitourinary tract such as kidney, renal pelvis, bladder, and prostate is very rare. 
| > Case report|| |
The case we present here is about a 68-year-old woman had an abodominal ultrasonography for nonspecific abdominal pain. It showed a solid lesion in the left kidney. The computed tomography (CT) urogram revealed a well-circumscribed solid lesion in the left kidney [Figure 1]. There was minimal contrast enhancement. There was no renal vein involvement by the tumor or lymphadenopathy. CT chest was normal.
|Figure 1: Computed tomography image of left kidney with a well-circumscribed solid lesion|
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She did not have hematuria. Three of her children had undergone treatment for colorectal cancer. Another son of hers and her sister's son had died of lung carcinoma. Her physical examination was unremarkable. She underwent left open radical nephrectomy with a presumptive diagnosis of renal cell carcinoma and made an uneventful recovery.
The cut section of the removed left kidney showed a circumscribed, white, firm, and tumor [Figure 2]. The tumor was 4.5 cm in its maximum dimension and confined to the upper pole. There was no capsular or hilar involvement.
Microscopically, the mass consisted of spindle cells with hypercellular and hypocellular areas [Figure 3]. The tumor cells contained oval to spindle shaped nuclei and scanty cytoplasm. No significant nuclear atypia or mitoses were seen. There was an area rich in numerous ectatic and interconnecting thin walled blood vessels. Entrapped renal tubules were seen at the periphery of the tumor. Rest of the renal tissue was unremarkable. Immunohistochemically, the tumor cells were diffusely positive for CD34 , CD99, and Bcl-2 [Figure 4]. The staining for cytokeratin, α-smooth muscle actin (α-SMA), and desmin were negative. The Ki67(c-kit) index was low (<1%).
|Figure 3: (a) The spindle cell lesion in relation to the normal renal cortical tissue (×100). (b) The spindle cell lesion showing the hypercellular and hypocellular areas (×400)|
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|Figure 4: Immunohistochemical staining: (a) CD 34, (b) smooth muscle actin, (c) Bcl-2, (d) desmin, (e) cytokeratin, (f) CD 99|
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Based on the histological and immunohistochemical features, a diagnosis of SFT of the kidney was established. Since there were no features of malignancy she was only followed-up. After 6 months she has no evidence of recurrences or metastases.
| > Discussion|| |
Solitary fibrous tumor is an uncommon spindle-cell mesenchymal tumor of probable fibroblastic derivation. It often presents a prominent hemangiopericytoma-like vascular pattern, but may exhibit other histological patterns.  SFTs arise most frequently in the pleura. However, occurrence at sites other than the pleura have been described in recent years. ,
The first case of renal SFT was reported in 1996.  Of the renal SFTs reported during the past 10 years, more than 50% have occurred in patients older than 40 years (from 33 to 76 years, with an average age of 52 years). , The male:female ratio is 1:1.5.  Most of these tumors were asymptomatic or having nonspecific vague symptoms. Hematuria, the characteristic symptom of renal carcinoma, is rare. Though hemangiopericytoma-like growth pattern is common, episodes of hypoglycemia reported with pleural SFTs are not described with renal SFTs.  Within the kidney, SFTs may arise from the renal capsule, cortex, pelvis, or peripelvic connective tissue.  In this case, the tumor was in the upper pole adjacent to the capsule. Hence, it could have arisen from the capsule or the cortex of the kidney.
The renal SFTs reported so far range from 2 to 25 cm (mean, 9 cm).  Macroscopically, renal SFTs are well-defined, pseudo-encapsulated, lobulated, and rubbery neoplasms. They have a homogeneous, tan-white, whorled cut surface without necrosis, cyst formation, or hemorrhage. 
The immunohistochemical study is the key to diagnosis. CD34 immunoreactivity has been reportedly shown to be strongly and diffusely expressed in many cases of SFT. Although, it is not specific for SFT, strong CD34 reactivity is currently regarded as characteristic and an indispensable finding in the diagnosis of SFT. 70% of SFTs express CD99 and Bcl-2. They lack the expression of cytokeratin, α-SMA, desmin, and s-100 protein. ,
Mesenchymal tumors that should be differentiated from renal SFT include sarcomatoid renal cell carcinoma, angiomyolipoma, fibroma, fibrosarcoma, leiomyoma, leiomyosarcoma, haemangioma, angiosarcoma, and gastrointestinal stromal tumor because these tumors typically show hemangiopericytomatous patterns. Diffuse positive expression of CD34, Bcl-2, and CD99 and negative expression of cytokeratin, α-SMA, S-100, CD31, and c-kit are useful for their differential diagnosis. ,
Electron microscopy may help in the diagnosis by differentiating tumor cells with fibroblastic features from those with muscular components.  However, there are no characteristic features in electron microscopy that will make a conclusive diagnosis of SFT.
Surgical removal remains the mainstay of treatment of renal SFTs.  Most cases reported so far had undergone radical nephrectomy since differentiation from carcinomas and sarcomas is difficult clinically and radiologically.
Although most cases are benign, the behavior of SFTs is unpredictable. Around 10-15% of pleural SFTs behave aggressively.  Only 10% are believed to be malignant when extrapleural. Malignant potential and long-term outcome of renal SFTs are not well established due to the paucity of cases. So far four cases of malignant SFTs have been reported from a total of about 40 renal SFTs reported. , Malignancy in renal SFT could occur in two ways. It may occur de novo or can follow dedifferentiation or sarcomatous overgrowth of an existing benign SFT.  The histopathologic features related to malignant behavior of renal SFTs include increased cellularity with crowded nuclei, cellular pleomorphism, increased mitotic activity (more than 4 mitoses/10 high power fields), necrosis, hemorrhage and high Ki-67 proliferative index. 
Clinical behavior of SFTs cannot be accurately predicted on histopathological basis with benign-appearing tumors exhibiting aggressive behavior and vice versa. , Therefore long-term follow-up of these patients is recommended to understand the natural history of renal SFTs better and to identify locoregional recurrences or metastases.
Genetic analyses of SFTs have not found consistent and characteristic cytogenetic abnormalities that can be used as an ancillary diagnostic marker.  However, occurrence of colorectal and lung cancers in several younger members of the family of this patient raise the possibility of an underlying genetic or familial predisposition. However, it is too premature to make any definitive comments about this until more similar cases are reported.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]