Prostate stromal tumor encompasses a rare neoplastic group originating from the specialized stroma of the prostate. The two most important subtypes are STUMP (stromal tumor of uncertain malignant potential) and malignant prostate stromal sarcoma. May show phyllodes tumor-like growth pattern — large, cystic-solid, mass deforming prostate contour. Originates from prostate mesenchyme and does not contain glandular epithelial component (pure stromal). On mpMRI, may show heterogeneous T2 signal, cystic-solid components, marked enhancement, and surrounding tissue invasion. In PI-RADS v2.1, it is in the differential diagnosis — solid stromal lesion may score PI-RADS 4-5. PSA usually does not rise because the tumor is stromal, not epithelial in origin.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Rare
Prostate stromal tumors originate from the hormone-sensitive specialized stroma of the prostate (fibroblasts, myofibroblasts, and smooth muscle cells). In normal prostate development, epithelial-stromal interaction under androgen influence directs glandular growth — in stromal tumors, this interaction is disrupted and the stromal component shows autonomous proliferation. The tumor is progesterone receptor (PR) and CD34 positive — these markers are also expressed in normal prostate stroma. In phyllodes-like growth pattern, stromal proliferation compresses glandular spaces creating leaf-like configuration — histological appearance similar to breast phyllodes tumor. Cystic changes result from retention cysts formed by stromal proliferation obstructing glandular ducts, or from tumor necrosis. On imaging, heterogeneous T2 signal reflects the coexistence of cystic (fluid → T2 bright) and solid (stroma → T2 intermediate-low) components. Marked enhancement results from intense vascularization in the stromal component. PSA not rising is because the tumor does not contain glandular epithelium that produces prostatic acid phosphatase and PSA.
The most characteristic morphological finding of prostate stromal tumor is the phyllodes-like (leaf-shaped) growth pattern. On T2-weighted MRI, low-intermediate signal solid stromal projections extend between high-signal cystic areas creating a leaf-like configuration — this pattern is identical to breast phyllodes tumor. Solid components projecting into cystic areas is explained by stromal proliferation compressing glandular spaces causing cystic dilatation. This morphological pattern is not seen in prostate adenocarcinoma (diffusely solid) or BPH (regular nodular) — it is a highly distinguishing finding for stromal tumor.
Large mass with heterogeneous signal on T2-weighted images. Solid components show intermediate-low T2 signal (stromal tissue), cystic components show high T2 signal (retention cyst or necrosis). Markedly deforms prostate contour. In phyllodes-like cases, leaf-shaped solid projections extend into cystic areas. Size usually >4 cm — rapid growth pattern.
Report Sentence
Large mass with cystic-solid components and heterogeneous T2 signal causing prostate contour deformity; stromal tumor (STUMP/phyllodes-like) should be considered in differential diagnosis.
Solid components isointense to prostate tissue on T1-weighted images. Hemorrhagic foci may be seen as T1 hyperintense areas. Cystic areas are T1 hypointense (simple fluid) or hyperintense (proteinaceous/hemorrhagic content). T1 signal variability in necrotic areas.
Report Sentence
Mass showing isointense solid component and focal hyperintense areas (hemorrhage) on T1-weighted images.
Marked, heterogeneous enhancement in solid components on contrast-enhanced sequences. Cystic areas show no enhancement. Prominent contrast difference at solid-cystic interface. Enhancement is more prominent than adenocarcinoma due to intense vascularization of stromal tumor. Necrotic areas show no enhancement.
Report Sentence
Marked heterogeneous enhancement in solid components and non-enhancing cystic areas with stromal tumor morphology.
Shows diffusion restriction in solid components on DWI — bright signal at high b-values and low signal on ADC map. No diffusion restriction in cystic components. ADC value in solid components may be as low as in adenocarcinoma (ADC <1.0 × 10⁻³ mm²/s), so DWI alone is not discriminatory.
Report Sentence
Diffusion restriction observed in solid components of the mass, no diffusion restriction in cystic components.
Large, heterogeneous, cystic-solid mass in pelvis on CT. Solid areas show enhancement, cystic areas remain at water density. Deforms prostate contour and may displace surrounding structures (bladder, rectum). CT is useful for evaluating tumor size, extent, and relationship to adjacent organs but does not provide tissue characterization as well as MRI.
Report Sentence
Large cystic-solid mass in pelvis on CT; MRI for tissue characterization and prostate stromal tumor evaluation is recommended.
Large, heterogeneous mass with cystic-solid components on TRUS. Solid areas of variable echogenicity (hypoechoic-isoechoic), cystic areas anechoic. Markedly enlarges prostate and disrupts normal zonal anatomy. Increased vascularity in solid components may be observed on Doppler.
Report Sentence
Large heterogeneous cystic-solid mass in the prostate on TRUS; detailed evaluation with MRI is recommended.
Criteria
Mild-moderate cellularity, sparse mitoses, minimal atypia. Malignant potential is uncertain — local recurrence possible (15-25%). Metastasis risk is low but not zero. Defined as a separate category in WHO classification. Long-term follow-up required.
Distinct Features
Low cellularity, sparse mitoses, recurrence potential, uncertain prognosis, long follow-up
Criteria
High cellularity, numerous mitoses (>10/10 HPF), marked atypia, necrosis. Aggressive behavior — local invasion, distant metastasis potential. Requires surgery + adjuvant therapy. Prognosis significantly worse than STUMP.
Distinct Features
High cellularity, many mitoses, necrosis, invasive, metastasis, poor prognosis
Criteria
Subtype showing leaf-shaped growth pattern. Morphology similar to breast phyllodes tumor — stromal leaves project into epithelial-lined spaces. May be STUMP or sarcoma grade. Tendency for large size and rapid growth. High recurrence rate after excision.
Distinct Features
Leaf pattern, large size, rapid growth, high recurrence, breast phyllodes analogue
Distinguishing Feature
Adenocarcinoma is diffusely solid, T2 hypointense, heterogeneous with marked diffusion restriction (low ADC). Contains no cystic component. PSA usually elevated. Stromal tumor is cystic-solid, phyllodes-like, and PSA normal. Morphological difference (cystic-solid vs diffusely solid) and PSA value are the most reliable distinguishing criteria.
Distinguishing Feature
Leiomyoma is entirely solid, homogeneously T2 hypointense with homogeneous enhancement — contains no cystic component. Stromal tumor is heterogeneous, cystic-solid, with heterogeneous enhancement. Leiomyoma is usually smaller and well-circumscribed. Homogeneity vs heterogeneity is the most important morphological difference.
Distinguishing Feature
BPH nodules show organized, regular nodular growth pattern in TZ. In BPH, prostate enlarges symmetrically and zonal anatomy is preserved. Stromal tumor disrupts zonal anatomy, creates asymmetric large mass, and shows cystic-solid structure. PSA may rise in BPH but proportional to volume — in stromal tumor, PSA remains normal.
Distinguishing Feature
Prostate abscess shows marked diffusion restriction in cystic component (purulent content), thick irregular wall and surrounding inflammation. Stromal tumor has no diffusion restriction in cystic components (simple fluid). Clinically, abscess presents with acute fever and sepsis while stromal tumor presents with chronic symptoms.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
3-monthProstate stromal tumors are rare but clinically important lesions. STUMP carries uncertain malignant potential — local recurrence rate is 15-25% requiring long-term follow-up. Stromal sarcoma shows aggressive behavior and requires surgery + adjuvant therapy. Definitive diagnosis is made by biopsy — transperineal or transrectal biopsy is performed when mpMRI findings raise suspicion. Normal PSA makes diagnosis challenging because standard screening algorithms for adenocarcinoma may not detect stromal tumors. In PI-RADS v2.1, cystic-solid mass scores PI-RADS 4-5. Surgical treatment includes radical prostatectomy or wide local excision. Adjuvant chemotherapy and radiotherapy are evaluated for sarcoma-grade lesions. Multidisciplinary tumor board evaluation is recommended.
Prostatic sarcomas are very rare but aggressive tumors. Rhabdomyosarcoma is more common in children, leiomyosarcoma in adults. Treatment is radical surgery + chemotherapy/radiation. Prognosis is generally poor. PSA is usually not elevated (non-epithelial tumor).