## Clinical Context This patient presents with obstructive jaundice, a pancreatic mass, and markedly elevated CA 19-9, consistent with pancreatic adenocarcinoma. ## Tumour Marker Profile in Pancreatic Cancer | Marker | Sensitivity | Specificity | Clinical Use | Pancreatic Cancer Relevance | |--------|-------------|-------------|--------------|----------------------------| | **CA 19-9** | 80–85% | 90% | Diagnosis, monitoring, recurrence detection | Gold standard for pancreatic cancer | | CEA | 40–50% | 95% | Non-specific; colorectal, lung, GI cancers | Low sensitivity in pancreatic cancer | | AFP | <5% | 99% | Hepatocellular carcinoma, germ cell tumours | Not elevated in pancreatic adenocarcinoma | | PSA | N/A | N/A | Prostate cancer | Irrelevant; patient has pancreatic cancer | ## Key Point: **CA 19-9 is the most sensitive and specific tumour marker for pancreatic adenocarcinoma.** It is elevated in 80–85% of cases and is used for: - Diagnosis support (when combined with imaging) - Monitoring treatment response - Early detection of recurrence post-resection - Prognostic stratification (higher levels = worse prognosis) ## Clinical Pearl: **CA 19-9 is a Lewis antigen-dependent marker.** Approximately 5–10% of the population lacks the Lewis antigen and will have persistently normal CA 19-9 despite pancreatic cancer; in such cases, CEA becomes the alternative marker. ## High-Yield: In this vignette, CA 19-9 at 1240 U/mL (>30-fold elevation) is diagnostic and will be the best marker to track during chemotherapy and post-operative surveillance. ## Warning: **CEA is NOT a first-line marker for pancreatic cancer** — it has low sensitivity (~40–50%) and is more useful in colorectal and lung cancers. AFP elevation would suggest hepatocellular carcinoma or a germ cell component, neither of which fits this clinical picture. 
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