Acid phosphatase (prostatic isoenzyme, PAP) was historically used as a tumor marker for prostate cancer. Which enzyme has now replaced it in routine clinical practice, and what is its major diagnostic limitation?

• A LDH isoenzyme 1; non-specific for prostate
• B Alkaline phosphatase; elevated only in bone metastases
• C 5-Nucleotidase; requires hepatic processing
• D PSA (prostate-specific antigen); non-organ specific, elevated in BPH and prostatitis ✓

Explanation

Prostate-specific antigen (PSA), a kallikrein-related serine protease, has replaced prostatic acid phosphatase (PAP) as the primary serum marker for prostate cancer. PSA is prostate-organ specific but NOT prostate-cancer specific — it is elevated in benign prostatic hyperplasia (BPH), prostatitis, and prostatic trauma. This lack of cancer specificity leads to false positives, overdiagnosis, and overtreatment, which is the principal limitation of PSA as a screening tool. Free PSA: total PSA ratio helps differentiate cancer from BPH.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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