Regarding the clinical utility and biochemical properties of common tumor markers, all of the following are true EXCEPT:

Explanation

## PSA: Production and Specificity **Key Point:** PSA is produced by BOTH benign and malignant prostate epithelium, not exclusively by cancer. This is a critical misconception that undermines the clinical utility of PSA as a screening tool. ### Biochemical Properties of PSA | Property | Details | |---|---| | **Source** | Benign prostate epithelium (90%), prostate cancer (10%), seminal vesicles | | **Type** | Serine protease; kallikrein-like enzyme | | **Function** | Liquefies seminal coagulum; not cancer-specific | | **Elevation in** | BPH, prostatitis, urinary retention, digital rectal exam, vigorous cycling, recent ejaculation | | **Specificity** | ~25% for cancer (at PSA 4–10 ng/mL, only 25% have cancer on biopsy) | | **Sensitivity** | ~80% in advanced disease; poor in early/localized cancer | **High-Yield:** PSA is organ-specific (prostate) but NOT cancer-specific. Benign conditions elevate PSA more than cancer in many cases. ### Why Each Statement Is Correct (Except Option 1) 1. **Option 0 (CORRECT):** CEA is elevated in colorectal cancer but also in: - Inflammatory bowel disease (Crohn's, ulcerative colitis) - Smoking (even in non-cancer patients) - Benign polyps, diverticulosis - Chronic lung disease **Clinical Pearl:** CEA is used for post-operative surveillance (rising CEA may indicate recurrence) rather than screening or diagnosis. 2. **Option 2 (CORRECT):** CA 19-9 is a Lewis blood group antigen-derived glycoprotein: - Elevated in pancreatic, biliary, gastric, ovarian cancers - Poor sensitivity for early-stage disease (~10–30% in stage I–II) - Useful for monitoring advanced disease and detecting recurrence - Also elevated in benign pancreatitis, cirrhosis, inflammatory bowel disease 3. **Option 3 (CORRECT):** hCG and AFP in germ cell tumors: - hCG: highly sensitive (>90%) and specific for choriocarcinoma and non-seminomatous germ cell tumors - AFP: highly sensitive for yolk sac tumors and non-seminomatous GCTs - Both are used for diagnosis, prognostication (IGCCCG risk classification), and monitoring treatment response - Excellent negative predictive value; persistently elevated hCG/AFP after chemotherapy indicates poor prognosis ### Why Option 1 Is Wrong Option 1 incorrectly states that PSA is produced "exclusively by malignant prostate epithelium." In reality: - PSA is produced by benign prostate epithelium in much larger quantities than by cancer cells - ~90% of PSA in serum comes from benign prostate tissue - PSA elevation is more commonly due to BPH, prostatitis, or urinary retention than to cancer - This lack of cancer-specificity is why PSA screening has high false-positive rates and leads to unnecessary biopsies **Warning:** Confusing PSA as cancer-specific is a common trap. PSA is organ-specific (prostate) but NOT disease-specific (cancer).