Abstract
Background/Aim: We present a case of solitary fibrous tumor, arising from the diaphragm in the retroperitoneal space, that was resected with robotic assistance. Case Report: An 85-year-old female patient was referred to our hospital for evaluation of a suspected right renal tumor. Abdominal contrast-enhanced computed tomography revealed a tumor (maximum diameter, 36 mm) protruding from the superior pole of the right kidney. The patient was scheduled for robot-assisted, retroperitoneoscopic, partial nephrectomy based on a preoperative diagnosis of renal cell carcinoma. Intraoperative findings revealed that the tumor originated from the diaphragm and had no continuity with the renal parenchyma. Pathological examination revealed a solitary fibrous tumor. Conclusion: Solitary fibrous tumors are rare soft-tissue neoplasms with a distinct molecular feature of the fusion of nerve growth factor-inducible A gene-binding protein 2 with signal transducer and activator of transcription 6 gene (NAB2::STAT6). We believe that this is the first reported case of a solitary fibrous tumor arising from the diaphragm in the retroperitoneal space.
- Diaphragm
- soft-tissue neoplasms
- solitary fibrous tumors
- retroperitoneal space
- robotic surgical procedures
- NAB2::STAT6
A solitary fibrous tumor (SFT) is a rare soft-tissue neoplasm of mesenchymal origin; it was first reported in 1931 by Klemperer and Rabin (1). SFT accounts for <2% of all soft-tissue neoplasms and develops most commonly in adults, and it has no sex predilection (2, 3). Although originally described as pleural tumors (2, 3), SFTs can develop anywhere in the body. We report a case of an SFT arising from the diaphragm in the retroperitoneal space that was successfully resected with robotic assistance.
Case Report
An 85-year-old female patient was referred to our hospital for evaluation of a suspected right renal tumor. Abdominal contrast-enhanced computed tomography revealed a tumor with a maximum diameter of 36 mm protruding dorsally from the superior pole of the right kidney with slight contrast enhancement (Figure 1A). Contrast-enhanced magnetic resonance imaging revealed an isointense tumor on T1-weighted images, marginal hyperintensity on T2-weighted images, and hyperintensity on diffusion-weighted images (Figure 1B-D). The patient was scheduled for robot-assisted retroperitoneoscopic partial nephrectomy using the da Vinci Xi® Surgical System (Intuitive Surgical, Sunnyvale, CA, USA) because of the preoperative diagnosis of renal cell carcinoma. The robotic procedure was performed in a 4-arm configuration with one assistant port. After establishing a 10-mmHg pneumoretroperitoneum, a 30° endoscope was inserted through the second port to commence the robotic procedure. The lateroconal fascia was incised and the right renal artery was identified, dissected, and secured using a vessel loop. The tumor was identified on the cephalad side of the kidney, and the renal parenchyma surrounding the tumor was dissected; however, no continuity between the tumor and the renal parenchyma was observed. Upon dissection of the tumor, it was observed that the diaphragm was the origin of the tumor (Figure 2A). Tumor resection was performed with a combination of hot and cold dissections using monopolar scissors (Figure 2B-D). The operative time was 71 minutes, and blood loss was minimal; no drain was placed postoperatively. The convalescence was uneventful, and the patient was discharged on postoperative day 6.
A: Contrast-enhanced computed tomography showing a tumor protruding dorsally from the superior pole of the right kidney with slight contrast enhancement (arrowhead). B: T1-Weighted fat-suppressed magnetic resonance imaging. C: Contrast-enhanced magnetic resonance imaging with fat suppression. D: T2-Weighted magnetic resonance imaging.
Intraoperative findings. A: Before resection, the tumor was observed to originate from the diaphragm (arrowhead). B and C: Dissection of the tumor from the diaphragm using monopolar scissors. D: After tumor resection.
Macroscopically, the tumor was well-defined and partially encapsulated with a pale reddish white cut surface (Figure 3A). Microscopically, the tumor comprised ovoid to spindle-shaped cells, exhibiting a patternless pattern against a variably collagenous background stroma with a staghorn or hemangiopericytoma-like vascular pattern (Figure 3B and C). The tumor cells exhibited 1 mitosis per 10 high-power fields. Immunohistochemical examination was positive for CD34 and signal transducer and activator of transcription 6 (STAT6) (Figure 3D). The Ki-67 labelling index of the tumor cells was 10%. The surgical margins were negative. Therefore, the tumor was diagnosed as SFT.
Pathological findings. A: The tumor had a well-defined margin and was partially encapsulated, with a pale reddish white cut surface. B and C: The tumor comprised ovoid to spindle-shaped cells arranged in a patternless pattern against a variably collagenous background stroma with a staghorn or hemangiopericytoma-like vascular pattern. D: Immunohistochemical examination revealing positive staining for CD34 and signal transducer and activator of transcription 6.
Discussion
To the best of our knowledge, this is the first report of SFT originating from the diaphragm in the retroperitoneal space. SFT is an anatomically ubiquitous, rare mesenchymal neoplasm, with an incidence of one case per million persons per year (4, 5). Pathologically, SFT shows various findings and is typically characterized by haphazardly arrayed spindle-shaped to ovoid cells, with irregularly branching staghorn-shaped thin-walled blood vessels and stromal collagen (6). Immunohistochemically, diffuse expression of STAT6 in the nuclei is pathognomonic for SFT (6).
A distinct molecular feature of SFT is nerve growth factor-inducible A gene-binding protein 2 (NAB2)::STAT6 fusion, which occurs due to a paracentric inversion in chromosome 12q. In 2013, three independent investigators identified NAB2::STAT6 fusion as the defining driver mutation in SFT (7-9). The NAB2::STAT6 fusion is believed to convert NAB2, which usually functions as a transcriptional repressor through its co-action with early growth response protein 1 (EGR1), to a transcriptional activator via the transcriptional activation domain of STAT6. The transcriptional product of NAB2::STAT6 functions as a transcriptional activator and induces the expression of the target gene (EGR1) resulting in constitutive activation of growth factors, including insulin-like growth factor 2 and fibroblast growth factor receptor 1 (7-9). Multiple variants of the NAB2::STAT6 gene fusion are known, and the fusion variant determines the morphology and clinicopathological characteristics of the SFT. SFT with the most common NAB2 exon 4::STAT6 exon 2 fusion variant occurs more often in the thoracic cavity, develops in older patients, and has less mitotic activity. In contrast, SFTs with the second-most common NAB2 exon 6::STAT6 exon 16/17 fusion variants often derive from the soft tissue of the pelvis and retroperitoneum, develop in younger patients, and have a higher mitotic activity. However, no prognostic impact has been shown for NAB2::STAT6 fusion variants (10, 11).
Surgical treatment is the mainstay of SFT management, similarly to most soft-tissue tumors. However, several retrospective studies have reported that the risk of metastasis was as high as 35-45% during long-term follow-up (2, 12). Many investigators have proposed risk stratification models, given the difficulty in predicting the clinical course of SFT (2, 3, 13). A retrospective study of 594 patients suggested that the addition of radiotherapy to surgery was significantly associated with a reduced rate of local failure (14). Several retrospective studies on advanced SFT that have evaluated the effectiveness of cytotoxic chemotherapy, such as doxorubicin, dacarbazine, and trabectedin, have reported limited response (15-17). Tyrosine kinase inhibitors, including sunitinib, pazopanib, and axitinib, are considered more effective than chemotherapy (18-20). The efficacy of pazopanib has been confirmed in phase II trials (19, 20).
Age, tumor size, mitotic activity and the presence of tumor necrosis are predictors of postoperative distant metastasis according to a frequently used risk model proposed by a retrospective observational study of 103 resectable SFT cases (2, 13), and our case was classified as having a low-risk, with a 10-year recurrence risk of 0%. However, a retrospective observational study of 31 cases of retroperitoneal SFT suggests that a Ki-67 index of ≥10% may be a predictor of tumor recurrence or metastasis (21). Long-term follow-up is also recommended in such cases because a recurrence at 23 years after surgical resection has been reported (22).
Conclusion
SFT is a rare soft-tissue neoplasm with the distinct molecular feature of NAB2::STAT6 fusion. To our knowledge, this is the first reported case of an SFT arising from the diaphragm in the retroperitoneal space.
Acknowledgements
The Authors would like to thank Enago (www.enago.jp) for English language review.
Footnotes
Authors’ Contributions
Toyoshi Seito: Conceptualization (lead); data curation (lead); writing – original draft (lead). Tomoyuki Kaneko: Conceptualization (lead); data curation (lead); writing – original draft (lead); writing – review and editing (lead). Taketo Kawai, Michio Noda, Yuumi Tokura, Itsuki Yoshimura, Mariko Yasui and Yoshinao Kikuchi: Data curation (supporting); writing – review and editing (support). Yuko Sasajima: Writing – review and editing (support); supervision (support). Tohru Nakagawa: Writing – review and editing (support); supervision (lead).
Conflicts of Interest
The Authors declare no conflicts of interest.
Funding
The Authors received no financial support for the research, authorship, and publication of this article.
- Received July 3, 2023.
- Revision received August 7, 2023.
- Accepted August 10, 2023.
- Copyright © 2023, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).
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