Abstract
Prostatic stromal tumors, encompassing prostatic sarcoma and stromal tumors of uncertain malignant potential (STUMP), represent an exceedingly rare category of prostatic diseases, with a prevalence of less than 1%. We present a rare case involving a man in his early 40s diagnosed with STUMP. Despite presenting with normal prostate-specific antigen (PSA) concentrations, the patient experienced persistent dysuria and gross hematuria for >7 months, leading to an initial misdiagnosis of benign prostatic hyperplasia. Persistent symptoms prompted further investigation, with magnetic resonance imaging (MRI) revealing a suspicious lesion on the left side of the prostate, initially thought to be malignant. Transrectal prostatic biopsy subsequently confirmed the presence of mucinous liposarcoma, with no medical history of diabetes, coronary heart disease, or hypertension. The treatment approach comprised robot-assisted laparoscopic radical prostatectomy, culminating in a postoperative pathological definitive diagnosis of STUMP. This case underscores the indispensable role of early MRI in the diagnostic process, highlighting the necessity of detailed pathological examination for a conclusive diagnosis. Our report aims to illuminate the diagnostic challenges and potential treatment pathways for STUMP, emphasizing its consideration in the differential diagnosis of prostatic tumors to advance clinical outcomes in this rare but important condition.
Keywords
Introduction
Prostatic stromal tumors are divided into prostatic sarcoma and stromal tumor of uncertain malignant potential (STUMP), which account for <1% of prostate cancers. 1 Prostatic stromal tumors are characterized mainly by atypical and distinctive mesenchymal cellular hyperplasia in the prostate gland and have been categorized as a specific mesenchymal tumor because of the unique development in prostatic tissue. 2 As a unique entity, these tumors include multiple subtypes. Early studies described STUMP as a prostate phyllodes tumor, atypical stromal hyperplasia, cystic liposarcoma, and cystic epithelial stromal tumor. 3 The age of patients with STUMP ranges widely from 23 to 81 years,4–6 and occurs mainly in those aged 50 to 70 years (Table 1). Typical clinical manifestations comprise urinary tract obstruction, hematuria, elevated serum prostate-specific antigen (PSA) concentration, and abnormal digital rectal examination findings, and may even affect sexual function. 7 In rare cases, STUMP may present as a huge bladder mass. 8 Five STUMP patterns have been described, including degenerative atypia matrix, a high density of spindle cells, and mucus-like spindle cells. The remaining patterns are a phyllodes-like pattern4,9,10 and a newly discovered round cell subtype, 11 of which degenerative atypia is the most common. However, the clinical presentation of STUMP varies widely, ranging from incidental findings to distant metastases and even death, and the great heterogeneity of its clinical behavior complicates the diagnosis. 12
Summary of previously reported cases of prostatic stromal tumors.
CD117, cluster of differentiation 117; CD34, cluster of differentiation 34; DRE, digital rectal examination; ER, estrogen receptor; PCa, prostate cancer; PR, progesterone receptor; PSA, prostate-specific antigen; RARP, robot-assisted radical prostatectomy; RCP, radical cyst prostatectomy; RP, radical prostatectomy; SMA, smooth muscle actin; SP, suprapubic prostatectomy; STUMP, stromal tumors of unknown malignant potential; TUB, transurethral biopsy; TURP, transurethral resection of the prostate.
Case report
We present the case of a man in his early 40s who experienced frequent urination, urgency, thin urine stream, weak urination, and other symptoms of dysuria without apparent triggers. Occasional hematuria but no low back pain was described, and the patient’s blood PSA concentration was normal. He had smoked for more than 20 years and denied drinking alcohol.
He was initially treated at the Social Welfare Hospital and underwent ultrasonography, which indicated prostatic hyperplasia. Although there was slight alleviation of the symptoms with medication, he continued to experience recurrent episodes of dysuria and eventually developed urinary retention, requiring an indwelling catheter. He was subsequently hospitalized, and upon rectal palpation, a firm nodule was detected in the left lobe of the prostate, with no obvious tenderness. Magnetic resonance imaging (MRI) revealed a left lateral prostatic mass (Figure 1) measuring approximately 24 × 22 mm, which was considered a malignant lesion. To clarify the diagnosis, we performed transurethral prostatic biopsy, and the pathology of the aspirate indicated prostatic mucinous liposarcoma, which was considered stage T2bN0M0. To obtain a precise diagnosis, we performed robot-assisted laparoscopic radical prostatectomy under general anesthesia.

Magnetic resonance images; ((a) coronal view and (b) transverse view): The prostatic volume is increased above normal, and the images show mixed signals dominated by slightly high-intensity signals surrounded by a low-signal-intensity capsule. No obviously abnormal signals are evident in the remaining prostatic tissue, and the prostatic capsule is intact (arrows).
The pathological examination of the postoperative specimens revealed an enlarged left lobe of the prostate, with a greyish-white mass evident in the section. The primary mass was localized within the left lobe of the prostate, with a portion displaying a jelly-like and soft texture. The mass measured approximately 3.5 cm × 2.7 cm × 2.0 cm. Microscopic examination revealed the presence of heterogeneous round and spindle-shaped cells in a mucus background. Notably, a subset of these heterogeneous cells exhibited markedly increased nuclear-staining depth, consistent with the morphological characteristics of STUMP. Furthermore, immunohistochemical analysis revealed negative staining for smooth muscle actin (SMA), MyoD1, myogenin, S-100, and pan-cytokeratin , and the MDM2 gene was amplified. Conversely, there was some positive staining for progesterone receptors (PR), and staining was diffusely positive for cyclin D-dependent kinase 4, desmin, and cluster of differentiation 34 (CD34) (Figure 2). These findings further supported the diagnosis of STUMP.

Pathological and immunohistochemical findings; (a–f) Biopsy-obtained pathological sections (×400) showing heterogeneous round and spindle-shaped cells in a mucus background. Positive staining for (b) CD34, (c) PR, (d) CDK4, (e) desmin, and (f) MDM2 is widespread among the tumor cells. Staining in panel (a): hematoxylin and eosin. CD34, cluster of differentiation 34; PR, progesterone receptor; CDK4, cyclin D-dependent kinase 4.
Discussion
Initially, this patient’s prostatic puncture biopsy was diagnosed as mucinous liposarcoma of the prostate. This condition is often confused with STUMP, likely owing to the limited volume of a puncture biopsy specimen. Subsequently, after a postoperative pathological examination, the patient’s diagnosis was revised to STUMP. Most reported STUMP cases are solitary, with only a tiny fraction co-occurring with prostatic adenocarcinomas.13,14 Early clinical symptoms in patients with STUMP are unremarkable. When the tumor is large, it may exert pressure on the bladder, and patients may have symptoms such as frequent urination, urgency, and dysuria. Compression of the lower ureter can cause hydronephrosis, and compression of the rectum leads to difficult bowel movements or an anal bulge, and scrotal and inguinal radiating pain. Rectal palpation of the prostate mainly reveals apparent prostatic enlargement, disappearance of the central sulcus, uneven surface, medium texture, and tenderness.
The primary imaging modality for evaluating STUMP is MRI, which typically reveals a solid appearance of the tumor with occasional findings of small focal cystic changes or minor focal hemorrhages. 15 These lesions show a consistent pattern, characterized by uniform low signal intensity on T1-weighted images, heterogeneous signal intensity on T2-weighted images, 16 slight hyperintensity on diffusion-weighted imaging, slight hyperintensity on apparent diffusion coefficient mapping, and specific features of continuous or gradual enhancement. 15 It is important to note that PSA is produced by prostatic epithelial cells, whereas stromal tumors originate from mesenchymal tissue, which may not result in a marked elevation of PSA concentrations. However, in a previous case report of STUMP, the PSA concentration was >14.7 nmol/L, 17 which required differentiation from prostate cancer. Immunohistochemical analysis of STUMP typically reveals positive expression of markers such as CD34 and vimentin, 18 with varying degrees of positive staining for myogenic markers, such as SMA, desmin, and muscle-specific actin. 15 Given their origin in the hormone-dependent specialized mesenchyme, these tumors usually express PRs, while exhibiting lower expression of estrogen receptors. 19 Additionally, S100 protein and c-kit (CD117) are generally not detected in STUMP. 9
Both STUMP and prostatic stromal sarcoma (PSS) are derived from the prostatic mesenchyme, making the distinction between them complicated. These tumors share clinical similarities and both express PRs, while both lack estrogen receptor expression. 19 However, PSS typically exhibits a higher diffusion-weighted imaging signal and lower apparent diffusion coefficient signal in MRI compared with STUMP. 15 Notably, this difference is insufficient to clearly distinguish the two. Therefore, the differential diagnosis of STUMP and PSS relies mainly on histopathological characteristics and immunohistochemical markers. 20 For PSS patients, positive staining for myogenic antibodies such as desmin, SMA, and MyoD14,21 is common, whereas STUMP generally involves positive CD34 and vimentin expression. 21 Although the genetic characteristics of STUMP have not been fully elucidated, the literature reports chromosomal alterations across all histological subtypes of STUMP. The most common alteration is the loss of chromosome 10, followed by loss of chromosomes 9 and 7. 22
Currently, a unified and clear STUMP treatment plan has not been established, as the clinical manifestations of STUMP vary from individual to individual, and the patient’s age, tumor size, tumor growth pattern, and degree of invasion affect the treatment choice. Therefore, treatment must be individualized, Additionally the tumor can remain stable for many years without treatment;23,24 however, some STUMP patients may have local recurrence, 25 and a very small number of tumors may evolve into PSS. It is worth noting that compared with radical resection, patients who undergo transurethral resection of the prostate appear to be more prone to recurrence,5,26 and radical resection of the prostate provides hope for patients with early STUMP.27,28
We opted for Da Vinci robot-assisted total prostatectomy (RARP) as our surgical approach, driven by its multifaceted benefits. 12 RARP affords superior surgical visualization owing to its high-definition three-dimensional optics, enhancing intraoperative anatomical discernment and thereby minimizing surgery-associated adverse events. The ergonomic design of the robotic system allows for intuitive surgeon hand movements, mitigating surgeon fatigue and enhancing surgical precision and consistency. 29 Additionally, the RARP technique harnesses the principles of fascial anatomy, facilitating meticulous dissection of the prostate from adjacent structures; thus, diminishing the likelihood of leaving behind malignant tissue. 30 This precise dissection preserves vital structures, notably, the urethral sphincter and neurovascular bundles pertinent to erectile function; thereby, attenuating the risks of postoperative complications, such as urinary incontinence and sexual dysfunction. 31 Fluorodeoxyglucose-positron emission tomography may help assess the malignant potential of STUMP, as the accumulation of fluorodeoxyglucose in these tumors is usually low, which may help in the development of surgical plans. 32 Therefore, in the treatment and follow-up of STUMP, these factors must be considered comprehensively while considering individual patient conditions to achieve the best therapeutic effect.
Conclusion
The clinical presentations of STUMP vary widely, often leading to potential misdiagnosis as prostatic hyperplasia if the diagnosis is based solely on clinical symptoms. Although MRI is beneficial in the early diagnosis of prostatic stromal tumors, a definitive diagnosis remains reliant on pathological examination. Regarding the differential diagnosis, particular emphasis should be placed on distinguishing STUMP from prostatic mesenchymal sarcoma. Treatment strategies should be meticulously customized to each patient’s unique profile, necessitating long-term follow-up to optimize the overall prognosis for individuals affected by STUMP.
The reporting of this study conforms to the CARE guidelines. 33
Supplemental Material
sj-pdf-1-imr-10.1177_03000605241253756 - Supplemental material for Prostatic stromal tumor of uncertain malignant potential: a case report and literature review
Supplemental material, sj-pdf-1-imr-10.1177_03000605241253756 for Prostatic stromal tumor of uncertain malignant potential: a case report and literature review by Tao Zhu, Cong Yin, Cen Liufu, Jiahao Jiang, Junhua Luo and Yan Wang in Journal of International Medical Research
Supplemental Material
sj-pdf-2-imr-10.1177_03000605241253756 - Supplemental material for Prostatic stromal tumor of uncertain malignant potential: a case report and literature review
Supplemental material, sj-pdf-2-imr-10.1177_03000605241253756 for Prostatic stromal tumor of uncertain malignant potential: a case report and literature review by Tao Zhu, Cong Yin, Cen Liufu, Jiahao Jiang, Junhua Luo and Yan Wang in Journal of International Medical Research
Footnotes
Acknowledgement
The authors thank Professor Liangkuan Bi for his dedicated advice and assistance in the diagnosis of this case.
Author contributions
Tao Zhu conceived and designed the study. Cen Liufu and Jiahao Jiang provided administrative support. Junhua Luo provided study materials or patient data. Yan Wang collected evidence and supervised the study. Tao Zhu and Cong Yin analyzed and interpreted the data. All authors wrote the manuscript and provided final approval of the manuscript to be submitted.
Data availability statement
The data that support the findings of this study are available from the corresponding author (Junhua Luo) upon reasonable request.
Ethics statement
We obtained written informed consent from the patient described in this report. Institutional review board approval was not required because of the retrospective nature of the study.
Declaration of conflicting interests
The authors declare that there is no conflict of interest.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by grants from the Science Technology and Innovation Commission of Shenzhen Municipality [grant numbers JCYJ20220531094217040, JCYJ20220530150812027, and JCYJ20220531094207017], the Scientific Research Foundation of Peking University Shenzhen Hospital [grant number KYQD2023308], and the Shenzhen High-level Hospital Construction Fund and ‘San-ming' Project of Medicine in Shenzhen [grant number SZSM202111007]. All figures were created using Adobe Illustrator.
References
Supplementary Material
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