PSA (prostate-specific antigen) is used as a tumor marker for prostate cancer. What is the biochemical nature of PSA and why can it be elevated in benign conditions?
- A PSA is specific only to prostate cancer cells and never elevated in BPH
- B PSA is a steroid hormone receptor elevated by androgen stimulation
- C PSA is a glycoprotein with esterase activity; elevated in any condition increasing prostate epithelial secretion or disrupting the basement membrane ✓
- D PSA is elevated only when metastatic prostate cancer is present
Correct answer: C. PSA is a glycoprotein with esterase activity; elevated in any condition increasing prostate epithelial secretion or disrupting the basement membrane
Explanation
PSA (KLK3/kallikrein-3) is a serine protease (chymotrypsin-like) synthesized by prostate epithelial cells that liquefies seminal coagulum. In normal glands, PSA is secreted into ducts and little enters blood; the basement membrane is intact. In BPH, prostatitis, or cancer, disruption of glandular architecture allows PSA to leak into the circulation. PSA is thus organ-specific but not cancer-specific. The ratio of free PSA to total PSA (<10-15% suggests malignancy) improves specificity.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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