Atypical Small Acinar Proliferation (ASAP) in a Prostate MRI Era: Is the Confirmatory Biopsy a Vestige of the Past?

Purpose: To determine whether a confirmatory biopsy is necessary after multiparametric magnetic resonance imaging (mp-MRI) to identify clinically significant prostate cancer in patients with findings of ASAP on biopsy. Methods: We performed a retrospective review of patients diagnosed with atypical small acinar proliferation (ASAP) on systematic transperineal prostate needle biopsy between January 2017 and July 2024. Patients then underwent a confirmatory biopsy, with or without prebiopsy mp-MRI of the prostate. Patients with prostate imaging reporting and data system (PI-RADs) lesions ≥ 3 also underwent a concurrent targeted biopsy. The cancer detection rate was determined for patient cohorts based on their mp-MRI findings. Results: A total of 155 patients were diagnosed with ASAP, and 36 underwent confirmatory biopsy after a median of 18 months. Clinically significant prostate cancer (grade group ≥ 2) was diagnosed more frequently in patients with preconfirmatory biopsy mp-MRI showing PI-RADs ≥ 3 compared with patients without an mp-MRI study (OR 20.0; CI 1.9-213.8; P = .009). Conversely, the risk of detecting clinically significant prostate cancer was equivocal in patients with preconfirmatory biopsy mp-MRI showing PI-RADs ≤ 2 (OR 0.83; CI 0.05-15.07; P = .45). A secondary analysis was performed evaluating mp-MRI scores and PSAD (prostate-specific antigen density), which found that no patients with mp-MRI showing PI-RADs ≤ 2 and a PSAD ≤ 0.15 had clinically significant prostate cancer on confirmatory biopsy. Conclusion: Our data demonstrate that diagnosis of clinically significant prostate cancer at confirmatory biopsy is relatively high when mp-MRI shows PI-RADs ≥ 3. The data suggest that mp-MRI, especially when used in conjunction with PSAD, is a useful adjunct to identify who may safely avoid confirmatory biopsy and potentially reduce the number of unnecessary prostate biopsies in this setting.