Prostate gland & seminal vesicles

Mesenchymal tumors

Prostatic stromal tumor of uncertain malignant potential

Editorial Board Members: Maria Tretiakova, M.D., Ph.D., Bonnie Choy, M.D.
Kenneth A. Iczkowski, M.D.

Last author update: 4 February 2022
Last staff update: 14 October 2022

Copyright: 2003-2024,, Inc.

PubMed Search: STUMP [title] prostate

Kenneth A. Iczkowski, M.D.
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Cite this page: Iczkowski KA. Prostatic stromal tumor of uncertain malignant potential. website. Accessed June 16th, 2024.
Definition / general
  • Stromal tumor of uncertain malignant potential (STUMP) is a term that should be reserved for a category of benign lesions that almost never metastasize (Arch Pathol Lab Med 2008;132:1729)
  • Stromal neoplasms that involve only the prostate are a heterogeneous group including:
    • 2 benign entities: STUMP, leiomyoma with atypia
    • 2 malignant entities: stromal sarcoma, phyllodes tumor
Essential features
  • Rare prostatic tumors with stromal degenerative atypia featuring vacuolated nuclei
  • Some cases have cyst spaces (need to rule out phyllodes tumor) (Clin Nucl Med 2021;46:348)
  • May recur rapidly after incomplete resection; rarely progress to stromal sarcoma
  • Stromal hyperplasia with atypia (a synonym that some scholars consider preferable to STUMP) more distinctly separates it from malignant neoplasms (Pathology 2021;53:12)
ICD coding
  • ICD-10: N40.1 - benign prostatic hyperplasia with lower urinary tract symptoms
Clinical features
  • CD34, Ki67 and cytokeratin are the most helpful immunostains (see Positive stains below)
Radiology description
  • STUMP as a solid / cystic lesion, has high signal intensity on diffusion weighted images; STUMP is favored by restricted diffusion of FDG or low FDG accumulation by 18F-FDG-PET, correlating with no recurrence or metastasis (Eur J Radiol Open 2020;7:100233)
  • Conversely, a malignant lesion with proven metastases, classifiable as phyllodes tumor (cystic epithelial tumor), will show high diffusion and FDG accumulation (Clin Nucl Med 2021;46:348)
Radiology images

Images hosted on other servers:

Lesion: low FDG uptake

Prognostic factors
  • Proliferative index as measured by mitotic count or Ki67 may presage worse outcome, although if high enough, sarcoma should be considered
Case reports
Gross images

Case #269

STUMP, prostate cross section

Images hosted on other servers:

STUMP that eventually metastasized

Microscopic (histologic) description
  • STUMP is morphologically heterogeneous but STUMP should have rare to no mitotic activity and no necrosis
  • Atypical stromal cells insinuate between benign acini
  • 4 patterns of STUMP have been described, all featuring cells with degenerative / smudged chromatin (J Urol 2004;172:894, Am J Surg Pathol 2006;30:694):
    • Hypercellular stroma with scattered degenerative atypia featuring vacuolated nuclei and smudged chromatin (50% of cases) (see Micro image 1)
    • Hypercellular stroma with bland spindle stromal cells
    • Benign (phyllodes-like, similar to breast) leaf-like growth of hypocellular fibrous stroma surfaced by benign prostate epithelium
    • Myxoid stroma with bland cells, lacking the nodularity seen in benign hyperplasia (Am J Surg Pathol 1998;22:148, Am J Surg Pathol 2006;30:694)
  • STUMP may also have epithelial proliferations that mask its diagnosis: most commonly glandular crowding and prominent basal cell layer, followed in frequency by prominent papillary infolding (Am J Surg Pathol 2011;35:898)
Microscopic (histologic) images

Contributed by Kenneth Iczkowski, M.D., Theo van der Kwast, M.D. and Case #269
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STUMP in prostate biopsy that had cancer in other fields

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Hypercellular stroma

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Circumscription of nodule

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Degenerative atypia

STUMP positive for CD34

STUMP positive for desmin

STUMP positive for HHF35

STUMP with low index for Ki67

STUMP positive for progesterone receptor

Positive stains
Negative stains
Molecular / cytogenetics description
  • Variety of different somatic variants were detected by next generation DNA and RNA sequencing in 7 of 14 STUMP or prostatic stromal sarcoma (PSS) cases; this included genetic aberrations seen in specific mesenchymal tumors arising at other anatomic sites, including soft tissue and the uterus (Mod Pathol 2021;34:1763)
  • Both prostatic stromal sarcoma (all 4 cases) and STUMP (consistent with stromal hyperplasia with atypia - 7 of 8 cases) shared chromosomal aberrations by array comparative genomic hybridization (aCGH)
    • Most common was the loss of chromosome 13 followed by loss of chromosomes 14 or 10 (Mod Pathol 2013;26:1536)
    • Certain additional mutations such as CHEK2 and KTM2D favor benign entities, whereas TP53 and RB1 mutations favor malignant; this suggests that sarcoma and STUMP exist on the same spectrum of entities (Mod Pathol 2013;26:1536)
      • However, either mutations or rearrangements were detected via DNA sequencing in 10 of 10 cases for both STUMP and PSS (in which PSS included phyllodes pattern) (Mod Pathol 2021;34:1763)
  • However, the specificity of chromosome 13 and 14 has been questioned and whole exome sequencing found a variety of changes in STUMP and PSS, implying these are not specific for the entities (Mod Pathol 2021;34:2082)
Sample pathology report
  • Prostate, transurethral resection:
    • Stromal hyperplasia with atypia (or stromal tumor of uncertain malignant potential) (see comment)
    • Comment: Nuclear atypia is not present, other than degenerative features. The diagnosis is supported by CD34 positivity, a low Ki67 proliferation index and cytokeratin negativity. Sarcoma and carcinoma are ruled out. In the literature, this lesion may recur after complete excision but does not metastasize.
Differential diagnosis
Additional references
Board review style question #1

Expected features of STUMP include

  1. CD34 is negative
  2. Cytokeratin positivity
  3. Degenerative nuclear atypia with nuclear vacuolation
  4. Does not tend to recur after resection necrosis
  5. Necrosis
Board review style answer #1
C. Degenerative nuclear atypia is common to all 4 patterns of STUMP, with nuclear vacuolation in most

A. CD34 should be positive, ruling out smooth muscle tumor (but not sarcoma)
B. Cytokeratin positivity should prompt consideration of sarcomatoid carcinoma or carcinosarcoma
D. Does have a tendency to recur after resection, so a prior diagnosis of STUMP is important
E. Necrosis is a malignant feature and probably rules out STUMP

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Reference: STUMP
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