SFT is rare. It is seen in patients of all ages, but most often between 50 and 70 years [1
]. SFT was originally described as a serosa-associated tumor in the thoracic cavity, but in the past 20 years it has been recognized in numerous non-serosal, extrathoracic sites, including the male genitourinary tract. Prostatic SFT is extremely rare. To the best of our knowledge, only 21 cases have been reported to date in the English literature, as single cases (n = 12) [3
] and a series of 9 cases [14
]. Our case represents the first one with complete clinical, radiological and histological data and a long follow-up.
All cases are summarized in
. The median age of patients at the time of diagnosis was 60 years (range 21-87). Clinical symptoms of prostatic SFTs depend on the size (pathological size ranging from 5 to 15 cm) and extension of the tumor: 1 patient was asymptomatic [8
], whereas all others presented non-specific urinary and/or rectal symptoms (obstruction, pelvic pressure). One case presented with macroscopical hematuria, which required an emergency hemostatic transvesical prostatectomy. Serum PSA level was normal in all cases tested, and hypoglycemia, previously reported in a few cases of serosal SFT, was not observed in the 13 informative cases. Radiological imaging was useful for the diagnosis and staging, notably to locate the initial site of tumor development, whenever possible. Indeed, these tumors may invade the neighboring structures especially in the retrovesical space, causing difficulty in determining the organ of origin. Generally, the first imaging was US, either transrectal or transabdominal. Pelvic CT and above all MRI more frequently allowed to locate the tumor and to estimate better its locoregional extension before surgery. In our case, and as previously reported [3
], MRI findings strongly suggested a tumor origin in the prostate, followed by extension to adjacent organs (especially bladder). The proneness of pleural SFTs to be misdiagnosed is well known [15
]. Given the extra-pleural and thus unusual location, prostatic SFTs are even more prone to this problem and represent one of the least commonly found spindle cell tumors on prostatic needle biopsy or transurethral resection. Differential diagnoses are numerous: they include other prostatic benign and malignant tumors, as well as SFTs and other spindle cell tumors arising from adjacent organs (bladder, seminal vesicle, rectum) then invading the prostate, such as rectal GIST. Histological diagnosis of reported cases was provided by analysis of tumor sample, either after needle biopsy (17 cases), transurethral resection (2 cases), or surgical resection without any prior biopsy (4 cases). In all cases, definitive diagnosis was done by histological and IHC examination of the surgical resection specimen. Microscopical and IHC aspects of prostatic SFTs are similar to those of non-prostatic SFTs. In 2 cases (including ours), a small associated prostatic adenocarcinoma was concomitantly accidentally discovered [14
Twenty-two cases of prostatic SFT reported in the literature
Regarding the prognosis, 10-20% of pleural SFTs (so-called ‘malignant SFTs’) behave aggressively with local invasiveness and/or recurrences, and/or occasional distant metastases [15
]. Histological features used for evaluation of malignancy include large size (>5-10 cm), high mitotic count (>4 per 10 HPF), high cellularity, necrosis, hemorrhage, cytological atypias with pleiomorphism, and infiltrative growth pattern [15
]. However, these features do not always forecast an unfavorable clinical outcome. In a large series of pleural SFTs [15
], all patients with histologically benign lesions and half of those with malignant lesions (defined by the presence of one or more of the following criteria: cellularity, mitotic count, pleomorphism) were cured by simple excision. Classically, extra-pleural SFTs have a more indolent behavior and are most always defined as benign. However, some of them can display histological aggressiveness criteria and/or present local and/or metastatic relapses [2
]. Like SFTs, the clinical outcome of extra-pleural SFTs is unpredictable. This is confirmed for the prostatic location through the analysis of the 17 cases reported with available follow-up. Only 1 patient displayed a local relapse at 12 months from initial incomplete surgery [12
]. Two patients died from postoperative complications on day 1 and from an unrelated cause at 7 months, respectively. None of the 14 other patients did relapse after a follow-up ranging from 2 months to 10 years, although several of them, including ours (large tumor size, cellular areas and foci of necrosis), displayed aggressiveness criteria. The only patient who relapsed was the one with incomplete initial surgery [12
]. For many authors, the complete resection of the tumor, whatever its pleural or extra-pleural location, is the most important factor predictive of clinical outcome, implying that the malignant potential of SFTs should be assessed according to both the histological aggressiveness criteria and tumor resectability, keeping in mind that histologically benign and completely resected tumors still have long-term malignant potential. Of course, given the scarcity of reported prostatic SFT cases and the lack of long-term follow-up, no conclusion can be drawn. Additional cases with long-term follow-up are required to better establish prognosis of prostatic SFTs and reliable prognostic criteria.
Given the scarcity of prostatic SFT, data on optimal treatment are obviously limited. Given the possible aggressive behavior and the uncertainty regarding the prognostic factors, prostate SFTs should be removed by complete excision with negative margins, then carefully followed-up for tumor recurrence. Surgery consists generally in a nerve-sparing radical prostatectomy, especially in younger men, aiming at preserving sexual and urinary functions. Associated cystectomy should be reserved to the cases of bladder involvement like ours, where involvement was suspected during surgery. SFTs are relatively insensitive to chemotherapy and radiotherapy [19
]. In the literature, one patient received adjuvant radiation therapy after R2 resection.