Overdiagnosis of prostatic adenocarcinoma.

A wide variety of histopathologic mimics of prostatic adenocarcinoma have been recently described, which may cause overdiagnosis of malignancy. To our knowledge, the frequency and causes of overdiagnosis of prostate cancer have not been previously examined. Two pathologists evaluated the Mayo Clinic experience with small foci of stage T1a cancer diagnosed between 1960 and 1970 in an effort to identify cases that were overdiagnosed as cancer. Only cases with available diagnostic slides and blocks were re-evaluated, and immunohistochemical studies were obtained in select cases to confirm the amended diagnoses. Follow-up was obtained in all cases from patient medical records. We identified a total of 31 patients who were overdiagnosed with prostatic carcinoma from among a series of 150 cases initially diagnosed as well-differentiated stage T1a cancer (21% incidence). Patients ranged in age from 42 to 85 years, and the weight of the transurethral resections varied from 6 to 90 g. Findings misinterpreted as cancer included atypical adenomatous hyperplasia (8 cases), basal cell hyperplasia (8), atrophy (5), sclerosing adenosis (3), high-grade prostatic intraepithelial neoplasia (3), xanthogranulomatous prostatitis (2), florid cribriform hyperplasia (1), and post-atrophic hyperplasia (1). None of the patients received additional treatment for prostatic disease. Mean follow-up was 10.8 years; 14 patients were alive with no evidence of disease, 14 died of intercurrent disease without recurrent prostatic disease, and the status of 3 was unknown. We conclude that misinterpretation of prostate cancer in transurethral resection specimens results from overdiagnosis of small microscopic foci of hyperplasia, atrophy, prostatic intraepithelial neoplasia, and granulomatous inflammation. The incidence of overdiagnosis three decades ago was 21% of small foci in transurethral resections, usually resulting from the presence of undescribed pathological entities. Long-term follow-up revealed no evidence of recurrent prostatic disease.