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Prostatic Intraepithelial Neoplasia (PIN)

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Image B

  • Generally regarded as probable precursor lesion for prostate carcinoma.
  • Divided into low grade (mild dyplasia) and high grade Prostatic Intraepithelial Neopplasia (HGPIN, severe dysplasia).
  • HGPIN is detected in 80-100% of prostate harboring carcinoma.
  • Like in prostate cancer, TMPRSS-ERG fusion is also detected but at a lower rate in HGPIN (19%) than prostate cancer (~50%).
  • Histology:
    • Preexisting (non-invasive) ducts and acini, usually medium to large size, lined by crowded cells with abnormal cytologic features (image A).
    • Has 4 major architectural patterns: micropapillary (image B), cribriform, tufted (image C) or flat.
    • Nuclei often show stratification.
    • Has nuclear features similar to cancer.
    • Unlike cancer, contains basal cell layer either continuous or discontinuous (remember non cancerous glands always has basal cells).

Image C

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  • Immunohistochemistry: like in cancer AMACR is overexpressed, but unlike cancer basal cell markers (HMWK and p63)+ (image D).
  • Median risk of cancer following diagnosis of high grade PIN is 21%.
  • Presence of multifocal (>3) or bilateral HGPIN or associated with ASAP has higher risk for subsequent cancer.
  • Current recommendation is to repeat biopsy if HGPIN is identified in needle biopsy without cancer.
  • DDX: intraductal carcinoma (intraductal spread by cancer) of the prostate, which also has basal cells, high-grade secretory cells, and similarly has both AMACR and basal cell markers positivity.
    • Unlike HGPIN, intraductal carcinoma has larger expansile glands and neoplastic cells span the entire lumen.