Atypical Small Acinar Proliferation of the Prostate: 16 Years’ ExperienceIczkowski, Kenneth A. MD*; Bostwick, David G. MD, MBA†Pathology Case Reviews: May/June 2014 - Volume 19 - Issue 3 - p 147–153 doi: 10.1097/PCR.0000000000000035 Reviews Abstract Author Information Abstract: We first described atypical small acinar proliferation suggestive of, but not diagnostic of, adenocarcinoma (ASAP) of the prostate in 1997. Atypical small acinar proliferation suggestive of, but not diagnostic of, adenocarcinoma represents our inability to render an incontrovertible diagnosis of cancer in about 2% to 5% of sets of needle biopsies and has a 40% to 50% predictive value for a definite cancer diagnosis on repeat biopsy. In this review, we discuss the justifications for reaching a diagnosis of ASAP, the clinical significance of ASAP, the differential diagnosis of a minimal focus on cancer versus ASAP, ASAP occurring in conjunction with high-grade prostatic intraepithelial neoplasia, and the use of immunostains using triple cocktail cytokeratin 34βE12/p63/p504S which can resolve some—but not all—cases of ASAP. From the *The Medical College of Wisconsin, Milwaukee, WI; and †Bostwick Laboratories, Glen Allen, VA. The author has no funding or conflicts to declare. Reprints: Kenneth A. Iczkowski, MD, Department of Pathology, Medical College of Wisconsin, 9200 W. Wisconsin Ave, Milwaukee, WI 53226. E-mail: firstname.lastname@example.org. © 2014 by Lippincott Williams & Wilkins.