Solitary Fibrous Tumor of the Prostate Treated with Frozen-Section Supported Robot-Assisted Nerve-Sparing Radical Prostatectomy Open Access

Solitary fibrous tumors (SFTs) are spindle-cell neoplasms of fibroblastic or myofibroblastic origin [1]. The World Health Organization classifies SFTs as neoplasms with intermediate biological potential in terms of malignancy, with a low risk of metastasis [2]. SFTs were predominantly found in the thoracic pleura [1] but can also occur in any anatomic site [2]. Due to the diverse occurrences and anatomical presentations of SFTs, there is a paucity of data for treatment in extrapleural origins. An extremely rare origin of SFT is the prostate. Prostatic SFTs were reported in about only 20 cases worldwide [2‒17]. To the best of our knowledge, we are the first to present the case of a patient with prostatic SFT in Switzerland, and demonstrate the feasibility of robot-assisted laparoscopic radical prostatectomy (RARP) and bilateral nerve-sparing supported by frozen section examination Table 1.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. Moreover, the study was reviewed and approved by Ethikkommission Nordwest- und Zentralschweiz, approval number 2020-00323.

The patient was a 60-year-old man who presented to an outpatient clinic with acute urinary retention and was subsequently found to have an enlarged prostate in March 2021. According to the external report, the patient was initially treated with a transurethral catheter and antiphlogistic therapy, as well as an alpha-blocker due to suspected benign prostatic obstruction. The catheter insertion was described as uneventful and 1,000 mL of clear urine emptied promptly. The urine culture was negative. The PSA level was 3.92 ng/mL. The patient was discharged with transurethral catheter and was further referred to our department for further urological diagnostic workup.

Prior to the preplanned appointment in our department, the patient presented with gross hematuria, as well as left-sided hydronephrosis to our emergency department. The digital rectal examination revealed an enlarged indolent prostate, without further suspicion for prostate cancer. The ultrasound examination confirmed the correct position of the transurethral catheter and a bladder tamponade. The prostate was estimated to be 60 cc in size. Inflammatory signs and laboratories were negative. Urine culture was negative. The patient was otherwise healthy and reported of no other comorbidities, no regular medications, and family history of urological conditions and tumors was negative. Due to recurrent bladder tamponades despite thorough irrigation and tamponade evacuation, an emergency transurethral endoscopic evaluation, tamponade removal and coagulation, and eventually transurethral resection (TUR) of the prostate was discussed with the patient, who agreed to this procedure. Intraoperatively, diffuse venous hemorrhage from prostatic vessels around the bladder neck was detected, as well as significant and diffuse hemorrhage from a grossly enlarged, and tumor-suspicious prostate middle lobe (Fig. 1). Within the framework of the extensive bipolar coagulation and the history of prior acute urinary retention, TUR of parts of the suspicious prostatic middle lobe was performed. Otherwise, no suspicious lesions were detected in the urinary bladder. The postoperative course was uneventful. The catheter was removed before hospital discharge without residual urine in the bladder and the left renal pelvic calicectasia was regredient. Final histopathology of the TUR specimen revealed an incompletely resected SFT.

For further staging of SFT and to rule out secondary tumors provoking gross hematuria, thoracoabdominal computed tomography with intravenous contrast agent was performed. In the urographic phase of abdominal computed tomography, urothelial carcinoma of the right distal ureter was suspected. One month after hospital discharge, the patient was readmitted for further diagnostics including ureteroscopy and cytology, which invalidated the suspicion of urothelial carcinoma of the ureter.

After having ruled out secondary tumors, the patient was discussed in our interdisciplinary tumor board including specialists for sarcoma treatment, which recommended radical prostatectomy. Four weeks after TUR, further magnetic resonance imaging (MRI) of the pelvis was performed, for locoregional assessment of adjacent anatomical structures. MRI confirmed a tumor of the prostate (25 × 31 × 27 mm) prolapsing intravesically with no evidence of infiltration of the urinary bladder without evidence of penetration of the prostatic capsule or lymph node infiltration. Prior to surgical resection, a repeat flexible cystoscopy in local anesthesia was performed, in order to evaluate the distance between the SFT and the ureteric orifices. Here, a macroscopic recurrence of SFT within the original TUR zone could already be detected (online suppl. figure; for all online suppl. material, see https://doi.org/10.1159/000534088). Eight weeks after SFT diagnosis, a RARP with bilateral nerve sparing, supported by frozen section examination, was performed. The intraoperative frozen section examination was negative. Due to the proximity of the tumor to the ureteric orifices, a 6Fr Double-J catheter was retrogradely inserted in both ureters. Final histopathological examination of the specimen confirmed a complete resection of the SFT with negative surgical margins. The SFT had developed from the transition zone (Fig. 1). No secondary prostate carcinoma was detected.

The postoperative course was uneventful and without complications. Since no vesico-urethral leakage was demonstrated in cystography, the transurethral catheter was removed on the fourth postoperative day and discharged from the hospital on the fifth postoperative day. In the short-term postoperative follow-up, on 10 days after surgery, the patient already reported of a very good general condition and a good ability to micturate without incontinence and no pad use. The Double-J catheter was removed 6 weeks after RARP. The postoperative follow-up included a MRI of the pelvis at 3 months and then every 6 months postoperatively. At 3 months, no tumor recurrence was detected and the patient reported of full continence, satisfactory micturition and satisfactory erectile function. Six months postoperatively, the situation remained unchanged.

Prostatic SFT is an extremely rare disease reported in the current literature and no standardized surgical approach has been defined yet. Due to the tumor biology of SFT, locoregional recurrence must be expected in cases of positive surgical margins [2, 6]. Therefore, only a complete surgical resection increases the chance for a long-lasting recurrence-free survival. On the other hand, adjacent neurovascular structures and the urethral sphincter need to be spared in order to allow for adequate continence and recovery of sexual function. Here, we present the first case of a healthy 60-year-old man willing to undergo RARP with bilateral nerve sparing supported by frozen section. To the best of our knowledge, we are the first to demonstrate the feasibility and safety of this technique in prostatic SFT.

Similar to the previous case reports [2, 6‒17], our patient was in the same age range from 21 to 75 years (Fig. 1). Therefore, SFT seems to occur in all age groups. However, when calculating the age reports of all publications, the median age of diagnosis is 52. Therefore, we can assume that SFT of the prostate may predominantly occur in middle-aged patients. Unfortunately, the current literature lacks sufficient data to analyze further epidemiological risk factors for prostatic SFT. While some case reports mentioned medical history, no comprehensive analysis is available [2, 8]. However, for soft tissue tumors in general, risk factors such as radiation exposure, family cancer syndromes, as well as chemicals (vinyl chloride, a chemical used in making plastics), were reported by the American Cancer Society. These risk factors for soft tissue tumors could be potential risk factors for SFT. Large-scale investigations using, for example, national databases, are needed to analyze risk factors for prostatic SFT.

As presenting symptoms, obstructive urinary symptoms were also reported in all other existing studies, whereas PSA was in general not elevated or slightly elevated and ranged from 0.64 ng/mL to 3.92 ng/mL, which was also the case in the present patient (Fig. 1) [9, 12, 14‒16]. In consequence, the leading symptom of prostatic SFT seems to be obstructive urinary symptoms combined with non-elevated or slightly elevated PSA levels. The reason for the gross macrohematuria that occurred in the present case remains a matter of discussion. We are of the opinion that the macrohematuria was associated with catheter insertion and therefore iatrogenic since the grossly enlarged SFT lobe predisposed the patient for trauma due to the catheter. Furthermore, SFT itself may lead to neovascularization that further predisposes for venous bleeding. This hypothesis is also backed by the intraoperative findings that only displayed diffuse hemorrhage from the SFT lobe.

According to National Comprehensive Cancer Network (NCCN) guidelines, surgical resection is the therapy of choice in sarcoma, if the tumor is resectable [18]. SFT would be categorized to this tumor entity. Similar to our patient, most studies (Table 1) performed surgical resection, if the tumor was localized. In 9 cases radical prostatectomy was performed, in 4 cases cystoprostatectomy and in 4 cases enucleation (Fig. 1). When radical prostatectomy was performed, predominantly open surgery was chosen. However, with the advent of robot-assisted surgery, the option of RARP became feasible. Yang et al. [9] were the first to demonstrate the feasibility of nerve-sparing open radical prostatectomy. However, since Kayani et al. [2] demonstrated within a systemic review that positive surgical margins were associated with early recurrence, we decided to perform RARP with bilateral nerve sparing supported by frozen section examination, to reduce the risk of positive surgical margins and still provide the best outlook for early recovery of continence and potency in this otherwise healthy man. For the same reason, we are of the opinion that enucleation procedures put patients at higher risk for recurrence and therefore did not consider this approach. Moreover, we performed the robot-assisted approach since institutional data and high-volume center reported no difference in oncological outcome between RARP and retropubic radical prostatectomy [19‒21].

Finally, in our case report, we did not perform lymph node dissection in accordance with the informed consent of the interdisciplinary tumor board. Since literature on SFT of the prostate is scarce, previous reports and medical professionals relied on general principles and guidelines for the management of soft tissue tumors, as well as in terms of lymph node dissection. For soft tissue tumors in general, present guidelines (NCCN and American Association of Oncology [ASCO]) recommend not to perform lymph node dissection systematically [18, 22]. The decision to perform lymph node dissection depends on suspicious regional lymph nodes and on several other factors such as tumor size, grade, location, and risk of metastasis. Therefore, it is essential for clinicians managing SFT of the prostate to collaborate with multidisciplinary teams, to make well-informed decisions on a case-by-case basis. Additionally, reporting individual case experiences and outcomes in the medical literature can contribute to a growing body of knowledge that may eventually help shape specific guidelines for SFT of the prostate management. Taken together, RARP with bilateral nerve sparing supported by frozen section is a feasible therapeutic option to treat prostatic SFT, when preoperative MRI indicates an organ confined disease. Needless to say, SFT is a very heterogenous disease that deserves a case-by-case evaluation. However, our report is the first to call for a standardized approach and interdisciplinary discussion on how to treat prostatic SFT. Different scenarios should be discussed and evaluated by an expert committee, including surgeons specialized in treating sarcomatoid tumors. For example, it would be worthwhile to discuss the feasibility of frozen section examination in non-organ confined tumors, especially for those that appear to invade the urinary bladder. Eventually, a certainly much more invasive cystoprostatectomy might be omitted in the case of negative surgical margins in the urinary bladder. Furthermore, enucleation procedures should be scrutinized for their potential to harbor a higher risk of recurrence.

Our work is not devoid of limitations: our findings should be interpreted in the context of their retrospective nature. Furthermore, due to the lack of available data we cannot draw strong conclusions according to treatment standards of SFTs. Moreover, we do not have long-term follow-up data. Regarding the lack of available studies and patient numbers, further multidisciplinary studies or epidemiological databases should address this topic in order to increase knowledge on this orphan disease.

This case demonstrates the exceedingly rare case of SFT of the prostate, which was described in the literature in only 23 men worldwide. Here, we were the first to demonstrate the feasibility of bilateral nerve-sparing RARP supported by frozen section.

Our research complies with the guidelines for human studies and was in accordance with the World Medical Association Declaration of Helsinki. The participant was fully informed about our research and a written informed consent was obtained from participant for publication of the details of their medical case and any accompanying images. Further inquiries can be directed to the corresponding author. Moreover, the study was reviewed and approved by Ethikkommission Nordwest- und Zentralschweiz, approval number 2020-00323.

There was no external financial support for this study. The authors declare that they have no conflict of interest.

All authors meet the ICMJE requirements. This manuscript is in full compliance with the requirements of the journal. All authors of this research paper have directly participated in the planning, execution, or analysis of the study. In addition, they have read and approved the final version submitted. The contents of this manuscript have not been copyrighted or published previously and are not under consideration for publication elsewhere. They will not be copyrighted, submitted, or published elsewhere while acceptance by the Journal is under consideration. There are no directly related manuscripts or abstracts, published or unpublished, by any authors of this paper. Our research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Each of the coauthors and myself have nothing to disclose.

There was no external financial support for this study.

Lara Franziska Stolzenbach, Christian D. Fankhauser, Agostino Mattei, and Christoph Würnschimmel meet the ICMJE requirements. Lara Franziska Stolzenbach and Christoph Würnschimmel have directly participated in the planning, execution, analysis, and writing of the study. In addition, they have read and approved the final version submitted. Christian D. Fankhauser and Agostino Mattei provide and cared for study patients. Moreover, they reviewed the research critically for important intellectual content and gave their final approval of the version to be published.

Since we describe a case report, the data are not openly accessible. However, all data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.