Which marker is used to differentiate benign prostatic hyperplasia (BPH) from prostatic carcinoma (PC)?

• A. Total PSA
• B. Free PSA
• C. PSA density
• D. Prostatic acid phosphatase

Answer: (B)

Free PSA, the unbound portion of total PSA, is the best discriminator between benign prostatic hyperplasia and prostate cancer. Total PSA can be elevated in both conditions, so it alone isn’t enough to tell them apart. In benign conditions like BPH, a larger fraction of PSA is in the free form, whereas cancer tends to produce more PSA that is bound or complexed, lowering the free PSA percentage. By looking at the ratio of free PSA to total PSA (often expressed as % free PSA), clinicians can gauge cancer risk: a higher % free PSA favors a benign process, while a lower % free PSA raises concern for malignancy and may lead to biopsy. The other markers have limitations: PSA density depends on prostate size and imaging accuracy; prostatic acid phosphatase is less specific and mostly used historically for advanced cancer.