Prostate gland & seminal vesicles

Mesenchymal tumors

Prostatic stromal sarcoma



Last author update: 9 February 2022
Last staff update: 9 February 2022

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PubMed search: Prostatic stromal sarcoma free full text[SB]

See also: Stromal proliferation of uncertain malignant potential

Kenneth A. Iczkowski, M.D.
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Cite this page: Iczkowski KA. Prostatic stromal sarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/prostatestromalsarcoma.html. Accessed January 28th, 2023.
Definition / general
  • Prostatic stromal sarcoma (PSS) is a rare entity (Pathology 2013;45:104)
  • Usually presents with urinary retention; also abnormal digital rectal examination, hematuria or hematospermia, palpable rectal mass
  • Includes phyllodes tumors (like those in the breast) (Pathology 2021;53:12)
Essential features
  • Cellular pleomorphism exceeds that of stromal proliferation of undetermined malignant potential (STUMP)
  • Necrosis
  • Mitotic activity
  • Extension outside the prostate
Terminology
  • Phyllodes tumor, cystic epithelial - stromal tumor, cystadenoleiomyofibroma, cystosarcoma phyllodes
ICD coding
  • ICD-10: C61 - malignant neoplasm of prostate
Epidemiology
Sites
  • Prostate and periprostatic tissue
Etiology
  • Unknown
Clinical features
Diagnosis
  • Cellular pleomorphism, necrosis, mitotic activity, extension outside the prostate and metastasis rule out benign mimics
Laboratory
  • Serum PSA is usually normal
Radiology description
  • Lesion that became metastatic was distinguished by intense uptake on 18F-FDG PET imaging (Clin Nucl Med 2021;46:348)
    • This high intensity is in contrast to the benign entity of stromal hyperplasia with atypia, also called STUMP
  • MRI shows a multinodular mass with homogeneous or heterogeneous low signal intensity on T1 weighted imaging and heterogenous high signal intensity on T2 weighted imaging (Oncol Lett 2016;11:2542)
Radiology images

Images hosted on other servers:

T1 weighted axial MRI image

T2 weighted axial MRI image

Prognostic factors
Case reports
Treatment
Microscopic (histologic) description
  • Greater cellularity, mitotic activity, necrosis and stromal overgrowth than STUMP
  • Storiform and infiltrative growth pattern
  • Sarcomas are subdivided into low grade and high grade based on mitotic rate, necrosis and degree of atypia (Am J Surg Pathol 2006;30:694)
  • There may be either stromal elements with benign glands resembling malignant breast phyllodes tumors or pure stromal elements
Microscopic (histologic) images

Contributed by Kenneth Iczkowski, M.D.
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Phyllodes tumor: malignant epithelium

Positive stains
Negative stains
Molecular / cytogenetics description
  • Both prostatic stromal sarcoma (all 4 cases) and stromal hyperplasia with atypia (also termed STUMP) (7 of 8 cases) shared chromosomal aberrations by array comparative genomic hybridization (aCGH)
    • Most common was loss of chromosome 13 followed by losses of chromosomes 14 or 10 (Mod Pathol 2013;26:1536)
    • Additional mutations, such as CHEK2 and KTM2D, favored benign entities, whereas TP53 and RB1 mutations favored malignant (Mod Pathol 2013;26:1536)
      • This suggests 2 separate entities; however, either mutations or rearrangements were found via DNA sequencing in 10 of 10 cases of both STUMP and PSS, while only PSS included phyllodes pattern (Mod Pathol 2021;34:1763)
  • Also, 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 2 entities are part of the same spectrum (Mod Pathol 2021;34:2082)
Sample pathology report
  • Prostate, transurethral resection:
    • Prostatic stromal sarcoma (see comment)
    • Comment: Cells have marked nuclear atypia, mitotic activity and pleomorphism. Necrosis is present. Tumor is positive for CD34 and has high Ki67 index, confirming the diagnosis.
Differential diagnosis
Board review style question #1
If only 2 positive markers were chosen to rule in prostatic stromal sarcoma, what would they be?

  1. Desmin and S100 protein
  2. Estrogen receptor and CD34
  3. High Ki67 proliferation index and CD34
  4. S100 protein and STAT6
  5. Smooth muscle actin and estrogen receptor
Board review style answer #1
C. High Ki67 proliferation index and CD34. CD34 positivity rules out a smooth muscle tumor (leiomyoma, leiomyosarcoma) or synovial sarcoma, while a high Ki67 proliferation index rules out STUMP, which has a low index. Desmin (A) does not discriminate the sarcoma from STUMP. Estrogen receptor and CD34 (B) are mostly positive in both sarcoma and STUMP but do not distinguish them. S100 protein and STAT6 (D) are both negative in sarcoma and STUMP. STAT6 is specific for solitary fibrous tumor. Smooth muscle actin and estrogen receptor (E) do not discriminate sarcoma from STUMP.

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Reference: Prostatic stromal sarcoma
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