Background: Carbohydrate antigen 19-9 (CA 19-9) is the most widely used tumor marker in pancreatic ductal adenocarcinoma (PDAC). Beyond diagnosis it is frequently used for prognosis, monitoring response to therapy, and detecting recurrence, but its limitations (Lewis antigen negativity, benign causes of elevation) must be recognized.

Aim: To evaluate the prognostic value of baseline CA 19-9, peri-operative changes, and post-treatment trends in patients with pancreatic cancer and to correlate CA 19-9 dynamics with overall survival (OS), progression-free survival (PFS), resectability and response to therapy.

Materials & Methods: Retrospective/prospective cohort of consecutive PDAC patients (n = ___) treated at a tertiary cancer centre between YYYY–YYYY. Baseline CA 19-9 measured prior to any therapy. For surgical patients, CA 19-9 measured pre-op and at fixed intervals post-op (4–8 weeks, then every 3 months). For unresectable/metastatic disease, CA 19-9 measured every cycle or every 6–8 weeks. Primary outcomes: OS and PFS. Secondary: resection margin status, radiological response (RECIST), and recurrence. Statistical analysis: Kaplan-Meier survival curves, Cox proportional hazards, and multivariable models adjusting for stage, performance status, age, and treatment received. Significant p < 0.05.

Results (template): Elevated baseline CA 19-9 (> 37 U/mL) was associated with shorter median OS (e.g., 10 vs 18 months; p < 0.001). A >50% decline in CA 19-9 after neoadjuvant therapy or after 2–3 cycles of chemotherapy correlated with improved radiological response rate and longer PFS (median PFS 8 vs 4 months; p = 0.002). Failure of CA 19-9 to normalize after R0 resection predicted early recurrence. Persistently rising CA 19-9 preceded imaging-detected progression by median 6–8 weeks.

Conclusion: CA 19-9 is a useful prognostic and monitoring biomarker in PDAC when interpreted in the clinical context. Baseline levels, early decline on therapy, and postoperative normalization (or lack thereof) have independent prognostic significance. CA 19-9 should be used alongside imaging, clinical assessment and multidisciplinary decision-making. Confirmatory prospective, multicentre studies and integration with novel biomarkers (ctDNA, genomic signatures) may further refine prognostication.