S3525 Recurrent Carbohydrate Antigen 19-9 Elevation Associated With Marijuana Use: A Benign Mimicker of Pancreatic Malignancy

Introduction: Carbohydrate Antigen 19-9 (CA 19-9) is a serum tumor marker commonly used to assess pancreatic malignancy. However, benign elevations can occur. We present a case of recurrent CA 19-9 elevation temporally associated with marijuana use, with normalization upon cessation. Case Description/Methods: A 49-year-old man with hypertension and chronic marijuana use was referred for elevated CA 19-9 following abdominal pain. Vitals were stable; exam revealed a non-tender abdomen with normoactive bowel sounds. Labs: WBC 7.4 × 10³/μL, hemoglobin 15.9 g/dL, ALP 59 U/L, AST 36 U/L, ALT 31 U/L, total bilirubin 0.7 mg/dL, and normal renal function. CA 19-9 measured 61.43 U/mL. Magnetic resonance cholangiopancreatography (MRCP) showed normal pancreatic and biliary anatomy. Endoscopic ultrasound (EUS) revealed diffuse parenchymal atrophy, hyperechoic strands, and lobularity without calcifications, masses, or honeycombing. He was advised to stop cannabis. Three months later, CA 19-9 decreased to 55.05 U/mL. At 1-year follow-up, CA 19-9 rose to 78.49 U/mL. The patient admitted to resuming marijuana use. Repeat EUS and pancreatic biopsy revealed no new findings and no dysplasia. The CA 19-9 elevation was attributed to cannabis exposure. Social work support was engaged for cessation counseling. Discussion: This case illustrates a reversible, benign CA 19-9 elevation associated with marijuana use. While typically linked to pancreatic adenocarcinoma, CA 19-9 can rise in conditions such as cholestasis, pancreatitis, cirrhosis, or fibrosis. Potential mechanisms include inflammation-driven secretion, impaired clearance, or cannabinoid receptor-mediated modulation of pancreatic and hepatic activity. Tetrahydrocannabinol (THC) interacts with CB1 and CB2 receptors in the pancreas and liver, potentially affecting immune tone, enzymatic activity, and bile secretion. In this case, biomarker trends closely mirrored marijuana use, suggesting a possible causative relationship. Awareness of such benign causes is essential to avoid unnecessary invasive testing. Further research is needed to clarify the dose-effect relationship and underlying biochemical mechanisms.