Other malignancies
Stromal tumor of uncertain malignant potential (STUMP)

Author: Kenneth A. Iczkowski, M.D. (see Authors page)
Editorial Board Member Review: Maria Tretiakova, M.D., Ph.D.

Revised: 6 February 2018, last major update July 2017

Copyright: (c) 2003-2018,, Inc.

PubMed Search: STUMP [title] prostate
Cite this page: Iczkowski, K.A. Stromal tumor of uncertain malignant potential (STUMP). website. Accessed March 21st, 2018.
Definition / general
  • Stromal neoplasms that involve only the prostate are divided into stromal tumor of uncertain malignant potential (STUMP), stromal sarcoma and carcinosarcoma
  • STUMP, prior to 1998, was termed atypical stromal hyperplasia (Am J Surg Pathol 1998;22:148)
Essential features
  • Rare prostatic tumors with stromal degenerative atypia featuring vacuolated nuclei
  • Some resemble breast phyllodes tumors
  • May recur rapidly after resection; rarely progress to stromal sarcoma
Clinical features
  • Usually presents with urinary obstruction, followed by hematuria, hematospermia and rectal fullness
  • Many STUMPs are incidental findings and behave indolently
  • A minority recur after surgery or metastasize
  • Up to 46% reportedly recur without definitive surgery (Am J Surg Pathol 1998;22:148)
  • Microscopically, STUMP should have rare to no mitotic activity and lack necrosis
  • Atypical stromal cells insinuate between benign acini
  • CD34 and cytokeratin are the most helpful immunostains
Case reports
Gross images

Images hosted on PathOut server:

Case of the Week #269

Images hosted on other servers:

STUMP which eventually metastasized

Microscopic (histologic) description
  • Four patterns of STUMP have been described (J Urol 2004;172:894, Am J Surg Pathol 2006;30:694), all with degenerative / smudged chromatin:
    • Hypercellular stroma with scattered degenerative atypia featuring vacuolated nuclei and smudged chromatin (50% of cases) (Fig. 1)
    • Hypercellular stroma with bland spindle stromal cells
    • Benign phyllodes-like, similar to breast, with "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 which mask its diagnosis: most commonly glandular crowding, prominent basal cell layer, prominent papillary infolding (Am J Surg Pathol 2011;35:898)
  • STUMP arises from specialized, hormonally responsive prostatic stromal cells, thus hormonal receptor immunostains may be positive
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Kenneth Iczkowski, M.D.
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Fig. 1: STUMP, in a
prostate biopsy that
had cancer in other

Case of the Week #269:
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Fig. 4: Hypercellular stroma

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Fig. 5: Circumscription of nodule

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Fig. 6: Multinucleation

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Fig. 7: Degenerative atypia

Fig. 8: STUMP positive for CD34

Fig. 9: STUMP positive for desmin

Fig. 10: STUMP positive for HHF35

Fig. 11: STUMP with low index for Ki67

Fig. 12: STUMP positive for progesterone receptor

Images hosted on other servers:

STUMP which eventually metastasized

Various images

Positive stains
Negative stains
  • STUMP should be cytokeratin negative, ruling out sarcomatoid carcinoma
Differential diagnosis
Additional references
Board review 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
Board review answer #1
C. Degenerative nuclear atypia with nuclear vacuolation is common to all four patterns of STUMP.

A. CD34 should be positive, ruling out smooth muscle tumor.
B. Cytokeratin positivity should prompt consideration of sarcomatoid carcinoma.
D. There is a tendency to recur after resection, so a prior diagnosis of STUMP is important.
E. Necrosis is a more malignant feature and probably rules out STUMP.