Minimal Adenocarcinoma in Prostate Needle Biopsy Tissue

One of the major diagnostic challenges in prostate needle biopsy interpretation is definitive establishment of a malignant diagnosis based on a minimal or limited amount of carcinoma in needle biopsy tissue. Major and minor diagnostic criteria should be used for interpretation of small foci of carcinoma. The constellation of findings and a combination of the major and minor diagnostic criteria permit a definitive diagnosis of focal adenocarcinoma. The differential diagnosis of minimal prostatic adenocarcinoma in needle biopsy tissue is broad and includes many benign lesions. The benign entities most likely to be misdiagnosed as minimal prostatic adenocarcinoma are atypical adenomatous hyperplasia (adenosis) and atrophy. High-grade prostatic intraepithelial neoplasia and a descriptive diagnosis of focal glandular atypia or atypical small acinar proliferation also should be considered before diagnosing minimal adenocarcinoma. The most valuable adjunctive study for the diagnosis of minimal adenocarcinoma is immunohistochemistry using antibody 34betaE12, reactive against basal cell–specific high-molecularweight cytokeratins. Most cases can be diagnosed based on H&E-stained sections without this immunostain. Most minimal carcinomas in prostate needle biopsy tissue are of intermediate histologic grade, and most are indicative of pathologically significant carcinoma in the whole prostate gland. During the last 15 years, there has been a dramatic 5-fold increase in the number of American men diagnosed with prostate cancer. In 1985, there were 37,324 new cases. In the year 2000, it is estimated that 180,400 men will be diagnosed with this malignant neoplasm. 1 Since the primary approach for establishment of a definitive diagnosis of prostate cancer is histopathologic interpretation of transrectal 18-gauge needle core biopsy specimens, there correspondingly has been a vast expansion in the number of prostate needle biopsy specimens reviewed around the United States. This striking increase is due to multiple factors, including widespread use of serum prostate-specific antigen (PSA) as a screening tool, the aging of the American population, increasing public awareness of prostate cancer, and clinical use of the 18-gauge biopsy gun, which allows for relative ease of prostate gland sampling. Early detection efforts, including screening with PSA and digital rectal examination, also have resulted in identification of lower stage and smaller volume carcinomas of the prostate. 2,3 Furthermore, many prostate cancers detected by an elevated serum PSA level are impalpable, and needle biopsy sampling of the prostate gland is thereby not directed toward a mass. These elements have resulted in the challenging task for the histopathologist of diagnosing malignant neoplasms on the basis of a limited or minimal amount of tumor in the small diameter 18-gauge needle biopsy cores of prostate tissue. The focus of this review is histopathologic diagnosis of minimal or limited carcinoma in prostate needle biopsy specimens. Thorson et al 4 define minimal carcinoma in needle biopsy tissue as tumor less than 1 mm in greatest dimension. Another definition of minimal adenocarcinoma is cancer involving less than 5% of needle core tissue. 5 In the first