Stromal tumor of uncertain malignant potential (STUMP)

Prostate
Other malignancies
Stromal tumor of uncertain malignant potential (STUMP)

Author: Kenneth A. Iczkowski, M.D.

Editorial Board Member: Maria Tretiakova, M.D., Ph.D.

Topic Completed: 1 July 2017

Revised: 28 February 2019

Copyright: 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: STUMP [title] prostate

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Table of Contents

Cite this page: Iczkowski KA. Stromal tumor of uncertain malignant potential (STUMP). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/prostatestromalprolif.html. Accessed February 27th, 2020.

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

Epidemiology

STUMP occurs in a broad age range with median age of 58 years (Am J Surg Pathol 1998;22:148, J Urol 2004;172:894)

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)

Diagnosis

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

34 year old man with prostatic stromal tumor with fatal outcome (Rare Tumors 2010;2:e57)
56 year old man with recurrent prostatic stromal tumour of uncertain malignant potential (Ann Acad Med Singapore 2005;34:441)
59 year old man with a PSA of 7.9 (Case of the Week #269)
67 year old man with incidental prostatic stromal tumor of uncertain malignant potential (Urologia 2012;79:65)

Gross images

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

Contributed by Kenneth Iczkowski, M.D.

Fig. 1: STUMP, in a
prostate biopsy that
had cancer in other
fields

Case of the Week #269

Fig. 4: Hypercellular stroma

Fig. 5: Circumscription of nodule

Fig. 6: Multinucleation

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

Only a few immunostains are discriminatory for STUMP; others are not helpful:
- CD34 and vimentin are most often positive (CD34 positivity helps rule out smooth muscle proliferations)
- Optional immunostains are progesterone receptor and androgen receptor, which should be positive (Prostate 1990;16:245, Arch Pathol Lab Med 2008;132:1729)
- Variable staining for smooth muscle actin and desmin (J Urol 2004;172:894, Am J Surg Pathol 2006;30:694)

Negative stains

STUMP should be cytokeratin negative, ruling out sarcomatoid carcinoma

Differential diagnosis

Carcinosarcoma: has malignant epithelial (CK+) and stromal components
Sarcomatoid carcinoma: malignant stroma cells; epithelial cells are ERG+ (Histopathology 2015;66:898)
Stromal nodule of nodular hyperplasia / benign prostatic hyperplasia: hyperplastic, not atypical stromal cells

Additional references

Mod Pathol 2007;20:148

Board review style question #1

CD34 is negative
Cytokeratin positivity
Degenerative nuclear atypia with nuclear vacuolation
Does not tend to recur after resection necrosis
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.

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