Current prostate biopsy interpretation: criteria for cancer, atypical small acinar proliferation, high-grade prostatic intraepithelial neoplasia, and use of immunostains.

CONTEXT: The past decade has brought major changes in prostate biopsy sampling, interpretation, and reporting.
OBJECTIVE: To summarize current information on diagnostic decision making, Gleason grading, "atypical" diagnoses, and use of immunostaining. DATA SOURCES: Pertinent literature from 1985 to 2005 is reviewed, emphasizing recent findings.
CONCLUSIONS: Diagnosis begins by evaluating a focus of atypical single-cell layer lined acini according to the 3 minimal diagnostic criteria for cancer: an infiltrative pattern, nuclear enlargement and hyperchromasia, and prominent nucleoli. The Gleason score and linear extent or percent of each core containing cancer should be reported. Atypical small acinar proliferation suspicious for malignancy designates foci that have either qualitative or quantitative limitations in atypia precluding a definite cancer diagnosis. It has about a 3% incidence as an isolated finding. Contemporary studies indicate a 39% predictive value for cancer on repeat biopsy. Isolated high-grade prostatic intraepithelial neoplasia has a 3% to 14% incidence and predicts cancer on repeat biopsy in 23% of cases. Immunostaining for a marker of benign prostate (cytoplasmic keratin 34betaE12 or nuclear p63) and a marker of cancer (alpha-methylacyl coA racemase, clone P504S) may or may not resolve atypical small acinar proliferation diagnoses. Performance of 34betaE12 and P504S immunostains resolved 76% of atypical small acinar proliferation diagnoses per consensus of 3 urologic pathologists studied; a technical limitation is preservation of the focus in question on the levels used for immunostaining.