3515 - Exploratory Analysis of PET and CA 19-9 Response in Pancreatic Ductal Adenocarcinoma Outcomes: A Secondary Analysis of a Prospective Phase 2 Trial
Presenter(s)
K. A. Rummel1, A. H. Goenka2, W. S. Harmsen3, M. Truty4, C. Thiels4, C. C. H. Stucky5, T. Bekaii-Saab6, R. R. McWilliams7, R. M. Carr7, M. A. Timm8, J. B. Ashman9, W. G. Rule9, C. M. Callaghan1, M. G. Haddock1, C. L. Hallemeier1, T. T. W. Sio9, K. W. Merrell1, and K. R. Jethwa1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Radiology, Mayo Clinic, Rochester, MN, 3Department of Biostatistics and Health Sciences Research, Mayo Clinic, Rochester, MN, 4Department of Surgery, Mayo Clinic, Rochester, MN, 5Department of Surgery, Mayo Clinic, Phoenix, AZ, 6Department of Medical Oncology, Mayo Clinic, Phoenix, AZ, 7Department of Medical Oncology, Mayo Clinic, Rochester, MN, 8Mayo Clinic, Rochester, MN, 9Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ
Purpose/Objective(s): To evaluate the association of PET and CA 19-9 response after neoadjuvant chemotherapy (NAC) with clinical outcomes including overall survival (OS), progression free survival (PFS), and College of American Pathologists (CAP) treatment response score in patients with pancreatic ductal adenocarcinoma (PDAC) treated with hypofractionated chemoradiotherapy (CRT)
Materials/Methods: This is a secondary analysis of a prospective phase 2 trial of patients with M0 PDAC who received NAC (median 8 cycles, 90% FOLFIRINOX) followed by CRT (45Gy/15 fx). Patients were defined as CA 19-9 optimal responders (CO) if CA 19-9 decreased to <35 U/mL after NAC, starting from either >35 U/mL or 1–35 U/mL at baseline. Suboptimal responders (CS) had CA 19-9 <1 U/mL (“non-secretors”) or remained >35 U/mL before and after NAC. Those with a hypermetabolic mass on pre-treatment or early PET scan (<4 cycles of NAC) with comparison post-NAC PET were included in PET-analysis. PET response was categorized as optimal (petO) if complete response, or sub-optimal (petS) if incomplete response or progressive disease. Univariate and multivariate analysis were performed to assess for association of CA 19-9 and PET response with OS, PFS, and CAP of 0-1. A p-value of <.05 was considered statistically significant.
Results: Of the 103 patients enrolled, 96 were included in the CA19-9 response analysis and 62 in the PET-response analysis. Median age was 66 years (range, 38-85), NCCN resectability status was 9% resectable, 43% borderline resectable and 48% locally advanced. Median baseline and post-NAC CA 19-9 were 65.5 U/mL (IQR: 17-283) and 25.0 U/mL (IQR: 9-64), respectively. 71 patients underwent resection with a 97% R0 rate. CAP of 0-1 was 28%. 49 patients (52%) were CO and 24 (39%) were petO.
There were no significant differences in OS (HR: 1.02; 95% CI, 0.63 - 1.66) or PFS (HR: 1.07; 95% CI, 0.68 - 1.69) for CO vs CS. The 2-yr OS, PFS, and CAP 0-1 were 57%, 33%, and 38% for the CO group compared with 52%, 31%, and 14% for the CS group. PetO was not associated with significant improvement in OS (HR: 1.30; 95% CI, 0.68 - 2.48), PFS (HR: 1.41; 95% CI, 0.79 - 2.53), or CAP 0-1 (OR: 0.64; 95% CI, 0.20 - 2.11). However, petO had numerically improved 2-yr OS, PFS, and CAP 0-1 (67%, 42%, and 41%) compared with petS (55%, 29%, and 31%). Combined CO + PetO was not associated with a significant difference in OS (HR 0.91, 95% CI, 0.45 - 1.83) or PFS (HR 0.71, 95% CI, 0.38 - 1.35). However, PetO + CO had numerically improved 2-yr OS, PFS, and CAP 0-1 of 67%, 44%, and 47% vs CS + petS of 58%, 30%, and 29%.Conclusion: Although statistical significance was not achieved, these data indicate that optimal PET and CA 19-9 response following NAC may correlate with improved CAP response and 2-yr OS. Given the limitations of sample size, these findings warrant validation in larger prospective cohorts and may inform future prognostic models in PDAC.