High-grade undifferentiated prostatic sarcoma with heterologous differentiation: A rare case report and literature review

Abstract

Primary prostatic sarcomas are extremely rare, accounting for less than 0.1 % of prostatic malignancies. They arise from mesenchymal stromal cells and exhibit aggressive behavior. We report a 45-year-old man with progressive lower urinary tract symptoms, abdominal distension, and weight loss. Imaging revealed a large pelvic mass inseparable from the prostate. Exploratory laparotomy showed a >30 cm encapsulated tumor, completely excised with partial prostate. Histopathology confirmed a high-grade undifferentiated sarcoma with heterologous differentiation. At two-year follow-up, the patient remained disease-free. Complete surgical excision remains the cornerstone of management, while multimodal therapy may be considered for high-risk or recurrent cases.

1. Introduction

Prostatic sarcomas are exceptionally rare, representing less than 0.1–0.2 % of primary prostatic malignancies. Unlike adenocarcinoma, they arise from mesenchymal stromal cells and include stromal tumors of uncertain malignant potential (STUMP), stromal sarcomas, and undifferentiated pleomorphic sarcomas.^1,2 According to the WHO Classification of Tumors of the Urinary and Male Genital Organs, 5th Edition (2022) (3), undifferentiated pleomorphic sarcoma (UPS) is defined as a high-grade malignant mesenchymal neoplasm lacking specific line differentiation. The present case fulfills these criteria and is best categorized as UPS of prostatic origin.

Patients typically present with urinary obstructive symptoms or a rapidly enlarging pelvic mass, while serum PSA levels usually remain normal.⁴ Imaging often reveals a large heterogeneous tumor, but histopathology with immunohistochemistry is essential for diagnosis. High-grade lesions are characterized by marked pleomorphism, brisk mitoses, necrosis, and sometimes heterologous differentiation.

These tumors usually follow an aggressive course with risk of recurrence and metastasis, though complete surgical excision remains the mainstay of management.² Given their rarity and lack of standardized treatment protocols, each case adds valuable information regarding clinical features, pathology, and outcomes.

This case is unique for several reasons: it represents the largest reported prostatic UPS (>30 cm) to date, demonstrated triple heterologous differentiation (lipoblastic, rhabdomyoblastic, and osteoid-like), and underwent complete surgical excision with negative margins. Such extensive multilineage differentiation has not been previously documented in a single prostatic sarcoma.

2. Case report

A 45-year-old male presented with a 9-month history of progressive lower urinary tract symptoms, including frequency, urgency, nocturia, dribbling, straining, poor stream, and a persistent sensation of incomplete bladder emptying. His symptoms worsened to the extent that he was voiding every 5–10 minutes. He also noted progressive abdominal swelling and un quantified weight loss.

At his local health center, catheterization was attempted but unsuccessful, and he was subsequently referred to Dessie Comprehensive Specialized Hospital, where he was admitted as an emergency. On examination, a large, firm, non-tender pelvic mass was palpable (Fig. 1). Digital rectal examination revealed an enlarged prostate with soft to firm consistency, without nodularity, and with its superior border not reachable. Serum PSA was 0.71 ng/mL (normal <4 ng/mL).

Fig. 1.

Preoperative photograph showing a markedly distended lower abdomen due to a large pelvic mass arising from the prostate.

Abdominopelvic CT demonstrated a large heterogeneous pelvic mass measuring 22 × 18 × 12 cm (Fig. 2), with pre-contrast and post-contrast attenuation values of 27 HU and 38 HU, respectively. The lesion compressed and displaced the urinary bladder anteriorly, was inseparable from the posterior prostate, and contained cystic components but showed no obvious local invasion. A provisional diagnosis of prostatic sarcoma was made.

Fig. 2.

Computed Tomography image showing a big pelvic mass.

Following counseling, the patient underwent exploratory laparotomy with palliative intent. Intraoperatively, a >30 cm smooth, soft, oval pelvic mass was identified, arising from the posterior wall of the prostate between the seminal vesicles (Fig. 3). The mass displaced the urinary bladder anteriorly and the ureters posterolaterally. No lymphadenopathy or local infiltration was seen. Complete excision of the tumor was achieved, including partial resection of the posterior prostate, right seminal vesicle, and right vas deferens (Fig. 4). The postoperative course was uneventful, and the patient was discharged on postoperative day seven.

Fig. 3.

Intraoperative finding showing a huge encapsulated pelvic mass arising from the posterior wall of the prostate and occupying the pelvic cavity.

Fig. 4.

Resected specimen of the prostatic mass showing a large, encapsulated tumor with areas of necrosis, hemorrhage, and heterogeneous cut surface.

Histopathological examination revealed a high-grade undifferentiated sarcoma, composed of spindle and pleomorphic cells, bizarre multinucleated giant cells, and areas with lipoblastic, rhabdomyoblastic, and osteoid-like differentiation. Brisk atypical mitoses and extensive necrosis were also noted.

At two-year follow-up, the patient had regained weight and remained asymptomatic. Surveillance CT and MRI scans demonstrated no evidence of local recurrence or distant metastasis.

3. Discussion

Primary sarcomas of the prostate are exceedingly rare, accounting for less than 0.1 % of all primary prostatic malignancies, with undifferentiated or unclassified sarcomas representing an even smaller subset.^1,2 These tumors originate from the mesenchymal component of the prostate and exhibit aggressive biological behavior, often presenting at an advanced stage with a large pelvic mass and obstructive lower urinary tract symptoms (LUTS).^2,4 The present case, characterized by a high-grade undifferentiated sarcoma with divergent differentiation (lipoblastic, rhabdomyoblastic, and osteoid-like elements), exemplifies this aggressive nature.

Patients typically present with rapidly progressive LUTS, urinary retention, or palpable pelvic masses, while serum PSA levels remain within normal limits, as observed in our patient (PSA 0.71 ng/mL). This aligns with existing literature indicating that PSA is usually not elevated in sarcomas due to their non-epithelial origin 4. Radiologically, these tumors often appear as large heterogeneous masses with cystic and necrotic areas, displacing adjacent structures without overt bone involvement—features consistent with previous descriptions of prostatic stromal and sarcomatous tumors.^2,5

The diagnosis hinges on histology, often supplemented by immunohistochemistry. Our case demonstrated spindle and pleomorphic cells with brisk mitotic activity and extensive necrosis, fulfilling criteria for a high-grade sarcoma. The presence of multiple lines of differentiation underscores the pluripotent nature of the originating mesenchymal cells, similar to observations in prior reports.^6,7 Ki-67 indices in reported cases range from 8 % to >25 %, correlating with aggressive clinical behavior.² The absence of epithelial markers such as PSA and the presence of mesenchymal characteristics further distinguish these tumors from poorly differentiated carcinomas. Table 1 summarizes reported prostatic sarcoma cases alongside the present case, highlighting clinical features, treatment approaches, and outcomes. Histopathological and immunohistochemical findings, including spindle and pleomorphic cells, mitotic activity, necrosis, Ki-67 indices, and mesenchymal marker expression, are emphasized to illustrate tumor aggressiveness and differentiation patterns.

Table 1.

Comparison of clinical features, management, and outcomes of reported prostatic sarcoma cases with the present case.

Author/Year	Age (yrs)	Histology	Tumor Size (cm)	Symptoms	PSA (ng/mL)	Treatment	Outcome
Gaudin et al., 19981	25–86	PSS/STUMP	5–14	LUTS, retention, hematuria	Normal	TURP/RP/RCP ± chemo/radiotherapy	3–72 mo survival
Cavaliere et al., 20146	14	High-grade PSS	6.5	Frequency, retention	N/A	Neoadjuvant chemo (IVADo) + surgery + RT	Died at 15 mo
Ueda et al., 20204	40	PSS involving rectum	5.5	Urinary distention	0.62	Pelvic exenteration + chemotherapy	Died at 10 mo
Osaki et al., 20038	65	PSS with epithelioid differentiation	5	Abdominal pain	Normal	Radical prostatectomy (no adjuvant therapy)	Disease-free at 8 yrs
Salih et al., 20239	21	High-grade PSS	9.1	Acute urinary retention	2.0	Radical cystoprostatectomy + chemo (AIM)	Died at 17 mo
Present Case	45	High-grade undifferentiated sarcoma	30+	Progressive LUTS, weight loss, mass	0.71	Complete excision (posterior prostate + SV)	Disease-free at 24 mo

The differential diagnosis includes leiomyosarcoma, rhabdomyosarcoma, stromal tumor of uncertain malignant potential (STUMP), and dedifferentiated carcinoma. Leiomyosarcomas typically express smooth muscle actin and desmin without lipoblastic or osteoid areas, while rhabdomyosarcomas show myogenin or MyoD1 positivity with rhabdomyoblastic morphology. STUMPs are lower-grade lesions lacking marked pleomorphism or necrosis. Dedifferentiated carcinomas may mimic sarcomas but retain epithelial markers such as cytokeratin and PSA, which were absent in our case.³

Surgical resection remains the cornerstone of treatment, aiming for complete excision with negative margins.^2,6 In our case, complete excision was achieved despite the tumor's size (>30 cm), which is exceptional given the technical challenges posed by pelvic organ displacement and vascular proximity. Literature indicates that even with aggressive surgery, local recurrence is common, and overall prognosis remains poor, with reported survival ranging from a few months to several years^8,9 Our patient's disease-free survival of 24 months post-resection without adjuvant therapy contrasts with the generally unfavorable outcomes seen in high-grade sarcomas, highlighting the potential benefit of early aggressive surgical management in selected cases.

The role of adjuvant therapy remains controversial due to the paucity of data. Chemotherapy regimens such as AIM (doxorubicin, ifosfamide, mesna) or IVADo (ifosfamide, vincristine, actinomycin D, doxorubicin) have shown partial responses in some reports, though with limited durability.^6,8 Similarly, adjuvant radiotherapy is recommended for large, high-grade soft tissue sarcomas to reduce local recurrence,¹⁰ yet its role in prostatic sarcomas is not clearly defined. In our patient, the absence of adjuvant treatment and the lack of recurrence at two year may suggest a possible role of radical excision alone in select scenarios, though this should not detract from considering multimodal therapy in high-risk patients.

Following complete excision, the patient was placed on regular surveillance. At 24 months postoperatively, there was no evidence of recurrence or metastasis. Prognosis remains guarded, as these tumors are associated with early recurrence and distant metastasis, most commonly to the lungs and, less frequently, to the liver and bone.^5,8 Long-term disease-free survival beyond two years is rare. Our patient's favorable short-term outcome underscores the importance of meticulous surgical resection and vigilant follow-up using MRI or CT to detect early recurrence.

4. Conclusion

High-grade undifferentiated prostatic sarcomas represent a diagnostic and therapeutic challenge due to their rarity, aggressive behavior, and lack of standardized treatment protocols. Our case highlights the critical role of early recognition, comprehensive imaging, and radical surgery in achieving temporary disease control. Given the high risk of recurrence, individualized multimodal strategies, including adjuvant chemotherapy and radiotherapy, should be strongly considered pending further evidence.

CRediT authorship contribution statement

Abenezer Bogale Abera: Writing – review & editing, Writing – original draft, Conceptualization. Lijalem Mekonnen Geremew: Writing – original draft, Conceptualization. Hailemaryam Shiferaw: Writing – review & editing, Conceptualization. Shiferaw Gedefa Fentie: Writing – review & editing. Yasin Worku: Writing – review & editing.

Declaration of generative AI and AI-assisted technologies in the manuscript preparation process

During the preparation of this work the authors used ChatGPT (GPT-5, OpenAI, 2025) for language editing and manuscript preparation assistance. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the published article.