Stains & molecular markers
Prostatic acid phosphatase (PAP, PSAP)


Topic Completed: 1 April 2012

Minor changes: 30 October 2020

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PubMed Search: Prostatic acid phosphatase [title] "loattrfree full text"[sb]

Nat Pernick, M.D.
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Cite this page: Pernick N. Prostatic acid phosphatase (PAP). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/stainspap.html. Accessed November 25th, 2020.
Definition / general
  • Prostatic acid phosphatase (PAP), also prostatic specific acid phosphatase (PSAP), is enzyme produced by prostate tissue
  • Acid phosphatases release phosphate groups, optimally at acid pH
  • May promote HIV infection
    • Naturally occurring fragments form amyloid fibrils (Semen-derived Enhancer of Virus Infection), capture HIV virions and promote their attachment to target cells (Cell 2007;131:1059)
Uses by pathologists
  • Identifies prostatic origin of metastases (whose primary is PAP+), including bone metastases (Ann NY Acad Sci 2011;1237)
  • Differentiates between prostatic and urothelial carcinomas
  • Differentiates between prostatic adenocarcinoma and mesonephric remnant hyperplasia (Ann Diagn Pathol 2009;13:402)
  • Presence is presumptive test for semen in forensic studies
Microscopic (histologic) images

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Various tissues

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Metastases, lymph node

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Metastases, soft tissue

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Prostatic adenocarcinoma

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Prostatic adenocarcinoma

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Prostate / colon in situ hybridization

Positive staining - normal
  • Prostatic epithelium (lysosomal granules) and prostatic ducts
  • May be expressed in non-prostatic tissue but at 1 - 2 orders of magnitude less than in prostate (Int J Clin Exp Pathol 2011;4:295)
Positive staining - disease
  • Prostatic adenocarcinoma and duct carcinoma (considered more sensitive but less specific than PSA)
  • PSA / PAP less sensitive in poorly differentiated adenocarcinoma (Am J Surg Pathol 1986;10:765, Am J Surg Pathol 1982;6:553)
  • PSA / PAP may become negative after hormonal treatment (Hum Pathol 1996;27:1377)
  • Bladder adenocarcinomas and rectal carcinomas may be strongly PAP+ but are PSA-
  • Bladder cystitis cystica / cystitis glandularis is occasionally positive (Arch Pathol Lab Med 1988;112:734)
  • Rectal carcinoids also positive for PAP, perhaps due to shared cloacal derivation of rectum and prostate (Am J Surg Pathol 1991;15:785); also ovarian strumal carcinoids
  • Salivary gland: pleomorphic adenoma (50%), duct carcinoma (20%)
Negative staining
  • Prostatic basal cells, urothelium, inflammatory cells
  • Nephrogenic adenoma of prostate, bladder, kidney (usually, may be weakly positive)
  • Mesonephric remnant hyperplasia (Ann Diagn Pathol 2009;13:402)
  • Prostatic clear cell adenocarcinoma
  • Nonprostate tissue and tumors other than those indicated above are usually negative / weak
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