Prostate gland & seminal vesicles
Benign mimickers of carcinoma
Adenosis / atypical adenomatous hyperplasia

Topic Completed: 1 May 2016

Minor changes: 11 August 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Adenosis / atypical adenomatous hyperplasia

Andres Matoso, M.D.
Komal Arora, M.D.
Page views in 2019: 5,338
Page views in 2020 to date: 3,284
Cite this page: Arora K, Matoso A. Adenosis / atypical adenomatous hyperplasia. website. Accessed August 12th, 2020.
Definition / general
Essential features
  • Characterized by a lobular proliferation of small glands
  • Similar to cancer, cells in adenosis may show small or medium size nucleoli, crystalloids, minimal infiltration and positive immunostaining for AMACR
  • In contrast to cancer, glands in adenosis have more pale cytoplasm, merge with adjacent larger benign glands, commonly has corpora amylacea
  • Basal cells can be identified in H&E stained slide or with immunohistochemistry for p63 or HMWCK
  • 2 - 20% of TURPs; 1% of prostate needle biopsies
  • More commonly in the transitional zone
Clinical features
  • Morphologic variant of benign crowded glands
  • A histologic finding only; does not have clinical implications
Prognostic factors
  • Not associated with increased risk of prostate cancer
  • One study showed no cases are positive for ERG by immunohistochemistry (Hum Pathol 2013;44:1895)
Case reports
Microscopic (histologic) description
  • Small, round, crowded, closely spaced acini mixed with larger acini with similar features within a circumscribed nodule
  • Complex and disorderly glands with an expansile or minimally infiltrative margin, crystalloids in up to 24%
  • Usually no prominent nucleoli, no blue tinged mucin
  • Normal sized nuclei, normochromasia, corpora amylacea common, may contain acidic mucin
  • Resembles Gleason 1 and 2 adenocarcinoma (Am J Surg Pathol 1995;19:737, Arch Pathol Lab Med 2010;134:427, Int J Surg Pathol 2005;13:167)
  • Lobular proliferation of small glands
  • Focal minimal infiltration in a proportion of cases
  • Glands with papillary infolding and branching lumina are common and helpful in differentiating from cancer
  • Budding of small glands from larger, more obvious benign glands
  • Clear cytoplasm
  • Occasional single cells or poorly formed glands are common; may represent tangential section of small glands
  • A prominent nucleoli can be seen but should not lead to the diagnosis of cancer; only huge nucleoli (> 3 micron) should raise concern for cancer
Microscopic (histologic) images

Contributed by Kenneth Iczkowski, M.D.

Atypical adenomatous hyperplasia

Images hosted on other servers:


HMWCK / 34betaE12

Positive stains
  • Mixture of CK903 positive and negative glands (i.e. glands with and without basal cell layer but discontinuous staining)
  • Basal cell markers (p63 and HMWCK) can be positive in a patchy fashion; AMACR may occasionally be positive
Negative stains
Differential diagnosis
  • In needle biopsies, may be mistaken for adenocarcinoma, Gleason pattern 3, but this has haphazard glands, often at right angles to each other
Board review style question #1

The diagnosis associated with this prostate biopsy is

  1. Best considered atypical small acinar proliferation, suspicious for malignancy
  2. Definitely benign
  3. Definitely cancer
  4. Probably cancer
Board review answer #1
B. Definitely benign. This is atypical adenomatous hyperplasia with small acini but lack of cytologic atypia and retention of basal cells.

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