One of the most common problems that interferes with the ability to make a definitive diagnosis is the size of the suspicious lesion. the currently used term prostatic intraepithelial neoplasia was later introduced by Bostwick and Brawer in 1987, and endorsed by consensus at a 1989 conference [3,4]. In recent years, many studies have ZNF346 shown that high-grade prostatic intraepithelial neoplasia (HGPIN) is the major precursor of prostate cancer. This review aims to clarify the diagnostic terms used in pathology reports and the implications the terminology has upon clinical management. Specifically, this article focuses on HGPIN as well as diagnostic terms L-690330 using the word atypical in the prostate. It is important to diagnose and correctly use the term HGPIN to avoid confusion with other atypical entities of the prostate, which may differ with respect to clinical significance. == Histologic Features == The term PIN encompasses morphologic changes in which prostatic epithelial cells are present in large and L-690330 branched glands, with a convoluted inner contour similar to non-neoplastic glands [1-2]. Epithelial proliferation produces a layer of crowded, pseudostratified cells with cytologic atypia, such as nuclear irregularity, nucleomegaly, hyperchromasia, and prominent nucleoli (Figure 1A). These cytological features are similar to those of invasive prostate cancer. However, in contrast to adenocarcinoma, the architecture of PIN is normal. PIN glands characteristically contain basal cells around their periphery (Figure 1B), seen as a thin and occasionally discontinuous layer on hematoxylin and eosin (H&E) stained sections [3-4]. This is an important diagnostic feature because the presence of basal cells can help to differentiate PIN from prostatic adenocarcinoma in which the basal cells are absent [5-8]. == Figure 1. == Comparison of HGPIN and adenocarcinoma.A.HGPIN (on the left) depicted by a large gland with multiple layers (pseudostratified) of proliferating neoplastic cells, while prostatic adenocarcinoma (on the right) is composed of small glands with a single layer of neoplastic cells.B.High power view of HGPIN showing nuclear atypia of the pseudostratified neoplastic cells with prominent nucleoli. A few flat basal cells, parallel to the basement membrane can be seen. PIN was originally subdivided into 3 groups which have now been combined into low-grade (PIN I) and HGPIN (PIN II and PIN III) [9]. HGPIN differs from low-grade PIN in that cytologic atypia is more apparent, particularly the presence of prominent nucleoli, as observed using a 20x-power lens (200-fold magnification). Because of its lack of clinical significance, low-grade PIN should not be included in a pathology report to avoid confusion with HGPIN which does impact clinical management. To correctly recognize HGPIN, it is necessary to be aware that there are several histologic patterns including tufting, micropapillary, flat, and cribriform. Other uncommon patterns (i.e., mucinous, signet ring cell, and foamy gland) have also been reported. The clinical significance of these different patterns is largely unknown [10-12]. Immunohistochemistry can aid in the diagnosis of HGPIN. Immunohistochemical staining of HGPIN for high molecular weight cytokeratins (HMWCKs) detected with 34bE12 antibody or p63 (Figure 2), easily demonstrates the presence of basal cells in HGPIN, which are lacking in prostatic adenocarcinoma as discussed above. Alpha-methylacyl-CoA racemase (AMACR) is a recently identified marker of prostate cancer with AMACR expression level much higher in adenocarcinoma than in non-neoplastic prostatic glands. Typically, prostatic adenocarcinoma shows strong AMACR staining while non-neoplastic prostatic glands have minimal to absent AMACR staining. However, within HGPIN, AMACR immunoreactivity ranges from minimal and weak to the strong staining characteristic of prostatic adenocarcinoma. Using the double-color triple-antibody (AMACR, HMWCK and p63) cocktail, HGPIN will demonstrate nuclear p63 and cytoplasmic basal L-690330 cell staining (brown) as well as cytoplasmic AMACR staining (red) (Figure 2B), which is different.