Suprarenal solitary fibrous tumor associated with a NF1 gene mutation mimicking a kidney neoplasm: implications for surgical management
© Conzo et al.; licensee BioMed Central Ltd. 2014
Received: 24 May 2013
Accepted: 15 March 2014
Published: 7 April 2014
Solitary fibrous tumor (SFT) is a rare spindle cell neoplasm, usually occurring in the pleura. Pararenal SFT, mimicking an adrenal gland or renal tumor, as here described, is extremely rare. We report a case of a right suprarenal SFT, incidentally discovered by abdominal ultrasound in a 54-year-old woman carrying a point neurofibromatosis 1 (NF1) gene mutation. Preoperative diagnostic work-up was ineffective in evaluating its origin, and an open radical right nephrectomy was therefore undertaken. Immunohistochemical assay showed a positivity for CD34, CD99 and Bcl-2, so suggesting a diagnosis of SFT. According to our knowledge, the association between this type of tumor and NF1 gene mutation has never been described. In cases of pararenal tumors, a more detailed preoperative diagnosis could be useful to better plan the extension of resection, allowing, in selected cases, nephron-sparing surgery. More studies are needed to better analyze the relationship between NF1 gene mutation and SFT.
Solitary fibrous tumor (SFT) is a rare spindle cell neoplasm, firstly described in the1930s. Prognosis seems to be favorable, but large series with long-term follow-up are still lacking. This kind of tumor, usually occurring in the pleura, the so called ‘localized fibrous mesothelioma’, has recently been described in different and multiple extrapleural sites including orbit, nasal cavity, breast, adrenal or thyroid gland, liver and lung. Although the retroperitoneum is frequently involved, according to a computed search of the medical literature, only 39 cases of renal or pararenal SFT have been reported. Tumor size ranged from 2 to 25 cm, and nephrectomy was the standard treatment. The origin of these neoplasms is still controversial[3, 4]. They are considered as slow-growing tumors with a favorable prognosis, although malignant cases, showing locoregional recurrence or distant metastases, have been reported. Neurofibromatosis type 1 (von Recklinghausen’s disease-NF1) is caused by an alteration of the NF1 gene, a tumor suppressor located on the long arm of chromosome 17 (17q11.2). Loss of the gene function, due to a point mutation, leads to an increase in cell proliferation and to development of tumors.
We describe a right suprarenal SFT in a female patient carrying a NF1 gene mutation. Preoperative diagnostic work-up was unable to determine its primal tissue, and therefore an open radical right nephrectomy was performed. Only the immunohistochemical assay allowed a correct pathological diagnosis. To better evaluate the role of radical nephrectomy, in a case of pararenal tumor with no clear signs of renal infiltration, more detailed therapeutic guidelines could be useful to establish the recommended extension of resection. According to our literature search, this is the first case in which SFT was associated to a NF1 gene mutation.
In most cases of SFT, described as renal or pararenal tumor, it is very difficult to determine the true origin from the renal capsule, the interstitial tissue, or the peripelvic connective tissue. Therefore, in planning a therapeutic protocol, extension of resection may be controversial and ‘classical’ nephrectomy remains the most common treatment. In the reported case, only definitive pathology identified a well-encapsulated SFT not infiltrating the kidney and the ipsilateral adrenal gland, and radical nephrectomy could probably be considered an overtreatment. Histopathological examination, immunohistochemical and ultrastructural studies are the cornerstone of SFT diagnosis. Morphologically, it is characterized by spindle cell proliferation, and about 70% of cases expresses CD 34, CD99, and Bcl-2; only between 20 and 35% of cases are variably positive for epithelial membrane antigen and smooth muscle actin. Focal and limited reactivity of S-100 protein, cytokeratins and/or desmin has also occasionally been reported. Strong CD34 reactivity is currently regarded as characteristic, and an indispensable finding in the diagnosis of SFT.
Since these tumors typically show hemangio-pericytomatous patterns, differential diagnosis includes sarcomatoid renal cell carcinoma or renal adenoma and other benign spindle cell tumors such as angiomyolipoma, fibroma, or fibrosarcoma. In presence of a NF1 gene mutation, neurofibroma should also be considered. SFT is a rare tumor sometimes mimicking renal cell or adrenal gland neoplasms[8, 9], and it must be considered in cases of renal tumors comprising mesenchymal elements. In roughly 10 to 15% of cases, they behave aggressively, showing local recurrence or distant metastases. According to England et al., increased cellularity with crowded/overlapping nuclei, cellular pleomorphism, and a mitotic count of more than four figures per ten high-power fields are considered criteria for malignancy. However, clinical progression of tumors with a benign appearance cannot be predicted on histopathological basis, which can exhibit aggressive behavior, and vice versa. Therefore, all SFT patients need to be on long-term follow-up[4, 7]. Turning to treatment, complete surgical resection is recommended, but because SFTs exhibit relative chemo-radio tumor resistance, no data are reported regarding the role of adjuvant treatment. In case of a preoperative suspicion of a well-encapsulated pararenal SFT, in the absence of clear signs of locoregional infiltration, the recommended extension of resection could be controversial. We hypothesize that, in selected cases, a nephrectomy could be avoided with comparable outcomes. The rarity of pararenal SFT does not allow randomized prospective trials concerning this issue. Preoperative diagnostic efforts must be made to achieve detailed data about its origin in order to plan a tailored surgery. The association of STF and the NF1 gene mutation is intriguing. However, since NF1 gene mutation has not been investigated systematically in STF cases, and the available evidence in the literature data is insufficient, it is hard to hypothesize how a gene mutation might determine the development of a suprarenal neoplasm. More studies are needed to better analyze the relationships between SFT and NF1 gene mutation.
Written informed consent was obtained from the patient for the publication of this report and any accompanying images.
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