This study was undertaken to determine retrospectively the prevalence and histologic features of the atypical foci that are suspicious for but are not diagnostic of a
malignancy in contemporary prostate needle biopsy specimens reported in a community practice. Histologic features were examined in detail to identify features that prevented an unequivocal diagnosis of
carcinoma. Of 1,009 prostate needle biopsy specimens obtained between January 1, 1993, and August 1, 1995, the diagnosis of an atypical focus suspicious for
malignancy was made in 48 (4.8%). In review of the biopsy specimens diagnosed as benign, an additional 7 cases (0.7%) were identified. The following histologic features were identified in 54 cases: enlarged nucleoli, 54 (100%); enlarged nuclei, 45 (83%); intraluminal eosinophilic secretions, 40 (74%); infiltrative growth, 37 (68%); small acinar proliferation, 37 (68%); intraluminal basophilic
mucin, 23 (42%); amphophilic cytoplasm, 18 (33%); high-grade
prostatic intraepithelial neoplasia, 17 (31%); and crystalloids, 12 (22%). Corpora amylacea were not identified. The foci contained from 1 to 67 acini (mean, 20.7). Although each atypical focus showed most of the features of
adenocarcinoma, an unequivocal diagnosis of
malignancy was not given owing to four features: the small size of the focus, the small number of cells with enlarged nucleoli, the clustered growth pattern, and the presence of high-grade
prostatic intraepithelial neoplasia within many of the foci. At initial examination, 36 of 41 patients (83%) had an elevated serum concentration of
prostate-specific antigen (mean, 10 ng/mL), and 20 (49%) had abnormal findings on a digital rectal examination. Twenty-five patients (46%) underwent additional sampling of the prostate, and 15 of these (60%) were found to have
adenocarcinoma; the remaining 30 patients did not undergo a subsequent biopsy. Patients with subsequent
cancer had higher mean serum concentrations of
prostate-specific antigen and change in concentrations of
prostate-specific antigen than those whose repeat biopsy results were negative; no other clinical or histologic differences were observed between these two groups. To the community pathologists in this study, the lack of prominent nucleoli, the small size of the focus, clustered acini, and/or adjacent high-grade
prostatic intraepithelial neoplasia prevented an unequivocal diagnosis of
malignancy. If a prostate needle biopsy specimen is reported as containing an atypical focus suspicious for
malignancy, a subsequent biopsy is warranted given the high predictive value for
adenocarcinoma.