Central zone histology of the prostate: A mimicker of high-grade prostatic intraepithelial neoplasia

The central zone (CZ) is located at the base of the prostate adjacent to the seminal vesicles. Its histology as a potential mimicker of high-grade prostatic intraepithelial neoplasia (PIN) has not been formally studied. Three groups were evaluated. Group 1 comprised 30 consecutive radical prostatectomy specimens assessed for the extent of CZ and of Roman arch and/or cribriform formation in the CZ. Group 2 comprised 100 consecutive cases of nonconsult prostate needle biopsies, screened in a random blinded fashion to identify CZ histology and the specificity of its identification on biopsy. Group 3 comprised 34 consult cases (1984 to the present) with CZ histology on needle biopsy. For group 1, the average maximum diameter of CZ histology was 5 mm. Two cases (6.7%) did not contain the classic features of CZ histology. The average amount of cribriform and/or Roman arch formation in the areas with CZ histology was 16.5%. In group 2, 10% of prostate needle biopsy cases had CZ histology. Of these, 80% were located on biopsy specimens designated as the base of the prostate, 10% were located in the base and midportion of the prostate, and 10% were located in the midportion of the prostate. For group 3, CZ histology occupied on average 32% of the involved core. The 2 most common histologic features were eosinophilic cytoplasm (97%) and location at the end of a core (97%). Other features were Roman arch formation (59%), a prominent basal cell layer (32%), cribriform formation (26%), and associated thick muscle bundles typical of bladder neck (24%). On average, cribriform and/or Roman arch formation occupied 22% of the CZ area seen on biopsy. Twenty-six of the consult cases were sent in with preliminary outside diagnoses. Of these, 21 (81 %) were either PIN or atypical: 11 (42%) high-grade PIN, 7 (27%) PIN, and 3 (12%) atypical glands. Our findings show that CZ histology is distinctive, as seen in radical prostatectomy specimens. Less frequently it is found on needle biopsy, where the presence of Roman arch and/or cribriform formation mimics PIN. Recognition of the distinctive features of CZ histology (i.e., tall columnar cells with eosinophilic cytoplasm, prominent basal cell layer, and lack of cytologic atypia) can help avoid a misdiagnosis of PIN or "atypia" on needle biopsy.