When can we use the Doubling Rule of PSA to Detect Prostate Cancer for BPH Patients who are treated with 5alpha-Reductase Inhibitor?

Since finasteride was available for benign prostatic hyperplasia (BPH), the PSA levels of the patients who were treated with 5alpha-reductase inhibitors (5ARIs) were investigated because of the decrease effect on PSA [1,2]. Because of the shrinking activity to the large prostate, 5ARIs have been used for reducing the risks of acute urinary retention and surgical operation. How can we screen prostate cancer of these patients? We know the doubling rule of PSA is available for the patients who were treated with 5ARI. But we do not know when this rule is actually and accurately available. The guidelines of BPH and prostate cancer do not provide the answer of this point. This issue is discussed here with some reports.