Abstract B29: Adjusting CA19-9 for biliary obstruction in pancreatic cancer

Background: Serum carbohydrate antigen (CA) 19-9 levels are often elevated in pancreatic cancer, and the degree of elevation has been used for de facto disease staging and prognostication. Previous studies and conventional wisdom suggest artificially elevated CA19-9 levels in the setting of obstructive jaundice, but the true incidence and degree of additional elevation is unknown. This study attempts to quantify the change in CA19-9 associated with relief of biliary obstruction via endoscopic stent placement in a pancreatic cancer patient population. Methods: Retrospective review of pancreatic cancer patients who underwent initial endoscopic stent placement for obstructive jaundice at a single, academic medical center from 2001 to 2011. Eligibility for this study included serum CA19-9 and total bilirubin (TB) levels within 10 days prior to and 30 days after endoscopic intervention. Patients with elevated CA19-9 and TB levels prior to endoscopy were included in analysis. Patients undergoing pancreatic surgery, chemotherapy, or radiotherapy prior to second CA19-9, or without post-stent decrease in TB, were excluded. Univariate analyses of patient and tumor characteristics by Fisher’s exact test. Patients who met above criteria were assessed by percent change in CA19-9. Results: Of 1,242 patients with pancreatic cancer, 627 underwent endoscopic procedures. In all, 16 patients had CA19-9 and TB levels both: 1) within 10 days prior to, and 2) within 30 days after initial endoscopic stent placement and a drop in TB, without interval pancreatic cancer-directed therapy. Initial CA19-9 levels varied from 82 u/mL to 48,122 u/mL with a median of 1,825 u/mL (IQR 346, 12,321). Median change in CA19-9 level was 26 u/mL (IQR -41, 7,056); percent change varied between -100% and 654% (median 11%; IQR -8%, 158%). The time between CA19-9 levels ranged from 1 to 31 days (median 13; IQR 10, 21). A single patient showed a dramatic drop in CA19-9. She experienced a 99.89% decrease in CA19-9, from 18,107 u/mL to 20 u/mL with 31 days between serum sampling. She was categorized as a remote outlier and removed from further analysis. Five patients demonstrated a drop in CA19-9, ranging from -1% to -31%. The median decrease was 120 u/mL (IQR -14, -588), and the median % decrease was 13% (IQR -7%, -15%; maximum drop 31%). Median days between CA19-9 was 11 (IQR 4, 11), with median time after stent to 2nd CA19-9 being 11 days (IQR 4, 11). Nine patients demonstrated an increase in CA19-9, ranging from 1% to 654%. The median increase was 3,250 u/mL (IQR 164, 20,297), and the median % increase was 95% (IQR 21%, 330%). Median days between CA19-9 was 16 (IQR 10, 21), with median time after stent to 2nd CA19-9 being 12 days (IQR 8, 20). Conclusions: CA19-9 is a serum biomarker used for risk prediction in pancreatic cancer among other gastrointestinal conditions. In the pancreatic cancer population, high CA19-9 levels are associated with worse long-term outcomes. In our cohort, the majority of patients did not have a decrease in CA19-9 following relief of obstruction. A subset of patients experienced large increases in CA19-9 despite effective stenting, which could represent disease progression. Based on our data, we propose a maximum 15% decrease in CA19-9 as a correction factor in the setting of obstructive jaundice to aid in pancreatic cancer prognostication. Citation Format: Lindsay A. Bliss, Douglas K. Pleskow, Mariam F. Eskander, Catherine J. Yang, Rebecca A. Miksad, Sing Chau Ng, Tyler M. Berzin, Mandeep S. Sawhney, Ram Chuttani, Jennifer F. Tseng. Adjusting CA19-9 for biliary obstruction in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B29.