Histological features and differential diagnosis of prostatic intraepithelial neoplasia

Prostatic intraepithelial neoplasia (HGPIN) is considered the most likely precursor of clinically significant prostate cancer. Biopsy remains the only definitive method for detecting these premalignant lesions. In this article we review the diagnostic criteria of HGPIN and discuss histological features that allow their distinction from other benign and malignant lesions. PIN is recognised at low power magnification as a thickened, basophilic and hyperchromatic epithelium in pre-existing acinar duct structures. This important histological feature is due to nuclear crowding and stratification. Distinction between HGPIN and tow grade PIN (LGPIN), a lesion with little clinical significance, is made mainly on the presence or absence of prominent nucleoli. HGPIN lesions always retain an intact or fragmented basal cell layer. The different growth patterns of HGPIN (tufting, micropapillary, cribriform and fiat) have no clinical significance but should be considered in the differential diagnosis together with normal structures, and both benign and malignant lesions. HGPIN has a high predictive value as a marker for prostate cancer but should not influence therapeutic decisions. Its identification in biopsy specimens warrants close surveillance with repeated biopsy.