CA 19-9 Maintains Prognostic Value for Inoperable Pancreatic Cancer Patients Receiving Definitive Hypofractionated or Stereotactic Body Radiation Therapy

Abstract

Use of carbohydrate antigen 19-9 (CA 19-9) in patients with resectable pancreatic cancer is well-established. The role of CA 19-9 in management of patients with inoperable pancreatic cancer receiving treatment with definitive hypofractionated or stereotactic body radiation therapy (SBRT) is less clear. Eligible patients for this IRB approved retrospective study included patients diagnosed with inoperable pancreatic cancer who received a definitive course of radiation therapy (RT) in either 50 – 52 Gy in 5 fractions or 50.7 – 67.5 Gy in 15 fractions. Patients were also required to have a recorded CA 19-9 value at diagnosis. Available CA 19-9 values were also recorded prior to radiation (within one month) and after RT (within 3 months). CA 19-9 levels were adjusted for bilirubin >2 mg/dL by dividing CA 19-9 level by bilirubin level. Overall survival (OS) was calculated from start date of RT. Patients were grouped based on CA 19-9 cutoff value of 90 U/mL (derived from literature). Kaplan-Meier curves were generated and differences between groups were determined using the log-rank method. Fisher’s Exact testing was performed to test correlation between CA 19-9 levels and likelihood of receiving a pancreatectomy. A total of 55 patients were eligible for this study (40 patients with locally advanced disease, 10 patients with borderline-resectable disease, and 5 patients who were medically inoperable). Median follow up was 13 months. Treatments included 5 fraction SBRT (n=15) or 15 fraction hypofractionated regimen (n=40). CA 19-9 levels were available for 51 patients prior to RT and 50 patients after RT. Median CA 19-9 levels were 121 U/mL (range: 1 – 9674) at diagnosis, 50 U/mL (1 – 29690) prior to RT, and 43 U/mL (1 – 28925) after RT. OS at 1 year was significantly improved with CA 19-9 level ≤ 90 U/mL at diagnosis (75% vs 59%, P=0.04), before RT (73% vs 48%, P=0.04), and within 3 months after RT (83% vs 25%, P<0.01). Fisher’s Exact testing did not identify significant correlation between likelihood of pancreatectomy and CA 19-9 levels at diagnosis (P=0.75), before (P=1.00) or after (P=0.46) RT (analysis excluded medically inoperable cases). CA 19-9 demonstrated a role as a prognostic marker for patients with inoperable pancreatic cancer receiving definitive hypofractionated/SBRT courses. CA 19-9 values do not appear to impact likelihood of undergoing a pancreatectomy after RT.