Prostate gland & seminal vesicles
Atypical / intraductal lesions
Low grade PIN

Editorial Board Member: Nicole K. Andeen, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Megan L. Brown, M.D.
Maria Tretiakova, M.D., Ph.D.

Topic Completed: 18 February 2021

Minor changes: 18 February 2021

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PubMed Search: low grade PIN [TIAB]

Megan L. Brown, M.D.
Maria Tretiakova, M.D., Ph.D.
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Cite this page: Brown ML, Tretiakova M. Low grade PIN. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/prostatelowgradePIN.html. Accessed May 16th, 2021.
Definition / general
  • Intraepithelial proliferation along pre-existing ducts and acini with mild atypia, at the lower end of the prostatic intraepithelial neoplasia (PIN) spectrum
  • Do NOT include in pathology reports - variability in diagnosis exists even among experts (Am J Surg Pathol 1995;19:873, Virchows Arch 2009;454:1)
Essential features
  • Not recommended to report
  • Often associated with high grade PIN
  • PSA may be elevated
Terminology
ICD coding
  • ICD-10: N42.31 - prostatic intraepithelial neoplasia I
  • ICD-10: N42.31 - prostatic intraepithelial neoplasia II
  • Synonyms: low grade prostatic intraepithelial neoplasia, prostatic intraepithelial neoplasia low grade
Epidemiology
  • Tends to be present in younger men, first appearing in men in their 30s - 40s (J Urol 1993;150:379)
  • No increase in prostate adenocarcinoma in patients with low grade PIN (risk of carcinoma on subsequent biopsy is 18%, as compared with 19% in a man with PSA levels of 4 - 10 ng/mL and an initial benign biopsy) (BJU Int 2011;108:1394)
Sites
  • No specific regions of the prostate
Pathophysiology
Etiology
  • None specific to low grade PIN
Clinical features
  • No specific clinical features
  • Associated with high grade PIN
Diagnosis
  • Seen incidentally on prostate biopsy
Laboratory
  • Elevations in PSA
Radiology description
  • Normal radiologic findings
Prognostic factors
Case reports
Treatment
  • No specific treatment recommended, treatment based on higher grade lesions
Gross description
  • No specific gross findings
Microscopic (histologic) description
  • Architecture:
    • At scanning magnification, darker and more complex than normal glands
    • Cellular crowding, pseudostratification with irregular spacing
    • Intact basal layer
  • Cytology:
    • Enlarged nuclei with increased variability in nuclear size and nuclear hyperchromasia
    • Indistinct and rare nucleoli
    • Amphophilic or eosinophilic cytoplasm
  • Reference: Virchows Arch 2009;454:1
Microscopic (histologic) images

Contributed by Nicholas P. Reder, M.D., M.P.H.

Acinar cells with crowded nuclei

Atypical acinar cells

Low grade PIN next to high grade PIN

Positive stains
Molecular / cytogenetics description
  • Usually diploid, in contrast with high grade PIN, which can be aneuploid
Sample pathology report
  • It is not recommended to report low grade PIN
Differential diagnosis
  • Benign central zone glands:
    • Can have complex architecture with papillary infoldings and pseudostratified epithelium but lacking nuclear atypia
  • Clear cell cribriform hyperplasia:
    • Clear cells forming crowded cribriform glands without atypia and with a very prominent basal cell layer
  • High grade PIN:
    • Prominent nucleoli (1 - 3 microns in diameter), robust cellular crowding and multilayering
  • Low grade PIN-like low grade prostatic adenocarcinoma:
Board review style question #1

The above finding may be regarded as low grade prostatic intraepithelial neoplasia. How should this be described in the pathology report?

  1. Benign central zone glands
  2. Clear cell cribriform hyperplasia
  3. Do not report, consider as no significant pathologic change
  4. High grade prostatic intraepithelial neoplasia
  5. Low grade prostatic intraepithelial neoplasia
Board review style answer #1
C. Do not report, consider as no significant pathologic change

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Reference: Low grade PIN
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