SUN-553 Abnormally High CA 19-9 in a Patient with Localized Pancreatic Cancer and Uncontrolled Diabetes Mellitus

Abstract Disclosure: L.J. Thaliath: None. J. Edmund: None. Introduction: CA 19-9 is a tumor marker used to diagnose Pancreatic cancer (PC), with sensitivity of 70%-90% and specificity of 68%-91%. It can also be elevated in nonmalignant conditions, like obstructive jaundice and inflammatory diseases, including Diabetes Mellitus (DM). We present a case of significant CA 19-9 elevation in a patient with resectable PC and high blood glucose levels. Case: 73-year-old male with a history of uncontrolled DM presented with jaundice and unintentional weight loss. Abdominal CT revealed ductal obstruction and a hypoenhancing mass in the inferior pancreatic head, raising suspicion for pancreatic adenocarcinoma. CA 19-9 was elevated at 2191 U/ml, and blood glucose was 264 mg/dl. Subsequent ERCP and EUS showed a 1.5 cm lesion abutting the distal common duct; a plastic biliary stent was placed, although brushings were non-diagnostic. A PET scan did not identify metastatic disease. Due to high suspicion of malignancy, repeat EUS and ERCP confirmed a 2.5 x 2.4 cm ill-defined lesion in the pancreatic head. Biopsy confirmed adenocarcinoma, and staging EUS indicated resectable disease. Despite biliary stent placement, CA 19-9 rose to 3743 U/ml, while blood glucose increased to 453 mg/dl. Repeat testing showed CA 19-9 dropping to 1818 U/ml as blood glucose fell to 234 mg/dl. The marked elevation in CA 19-9, despite localized disease on imaging, prompted neoadjuvant chemotherapy. Following three cycles of FOLFIRINOX, CA 19-9 decreased to 357 U/ml. After nine total cycles, the patient underwent a Whipple procedure, followed by three additional cycles. Postoperative imaging showed no evidence of metastatic disease. Discussion: A preoperative CA 19-9 level below 100 U/ml indicates resectable disease, whereas levels above 100 U/ml suggest unresectability/metastasis. We hypothesize that the abnormally high CA 19-9 in this patient, despite the absence of advanced/metastatic disease, may be attributed to hyperglycemia. This causal relationship is supported by the observed increase in CA 19-9 with rising blood glucose levels and a corresponding decrease in CA 19-9 levels with lower blood glucose. Studies show that hyperglycemia may lead to cellular changes in the pancreas, causing the release of CA 19-9 into the bloodstream. This case highlights the need for systematic assessment of CA 19-9 in patients with both DM and PC to refine its specificity and improve clinical outcomes. Presentation: Sunday, July 13, 2025