Atypical small acinar proliferation of prostate: Follow-up study of 114 patients

Background and aim: Atypical small acinar proliferation (ASAP) is defined as atypical foci suspicious for but not diagnostic of malignancy. ASAP is known as a strong predictive factor associated with prostate cancer. Because the diagnostic criteria for ASAP are subjective, objective diagnostic criteria were applied for ASAP as follows: (i) total loss of basal cells confirmed by immunohistochemistry and inconspicuous nucleoli; and (ii) a minute (≤500 micrometer in length) focus of atypical glands with total loss of basal cells and prominent nucleoli. Methods: To evaluate the cancer detection rate of ASAP diagnosed by objective diagnostic criteria, 114 patients initially diagnosed with ASAP were reviewed. Results: ASAP was noted in 2.17% of prostate biopsy cases. Eighty-one patients were successfully followed up. Twenty patients (24.7%) were finally diagnosed as having adenocarcinoma by subsequent biopsy. According to the criteria, we subclassified ASAP into two groups: ASAP (not otherwise specified [NOS]) and ASAP (suspicious microscopic adenocarcinoma). ASAP (NOS) and ASAP (suspicious microscopic adenocarcinoma) showed significantly different cancer detection rates (20.3% vs 71.4%) at subsequent biopsies (P= 0.003). Sixteen patients underwent radical prostatectomy, and 13 cases (81.2%) were categorized as clinically significant prostate cancer. Conclusions: The presence of ASAP in needle biopsy was evaluated to be an important predictor of cancer.