Carbohydrate Antigen 19-9 Response to Initial Adjuvant Chemotherapy Predicts Survival and Failure Pattern of Resected Pancreatic Adenocarcinoma but Not Which Patients Are Suited for Additional Adjuvant Chemoradiation Therapy: From a Prospective Randomized Study

Purpose: The predictive value of carbohydrate antigen 19-9 (CA19-9) for adjuvant chemo(radiation) therapy of resected pancreatic adenocarcinoma (PDAC) is undefined. Methods and Materials: We analyzed CA19-9 levels in patients with resected PDAC in a prospective randomized trial of adjuvant chemotherapy with or without additional chemoradiation therapy (CRT). Patients with postoperative CA19-9 ≤92.5 U/mL and serum bilirubin ≤2 mg/dL were randomized to 2 arms: patients in 1 arm received 6 cycles of gemcitabine, whereas those in the other received 3 cycles of gemcitabine followed by CRT and another 3 cycles of gemcitabine. Serum CA19-9 was measured every 12 weeks. Those who had CA19-9 levels always <3 U/mL were excluded from the exploratory analysis. Results: One hundred forty-seven patients were enrolled in this randomized trial. Twenty-two patients with CA19-9 levels always ≤3 U/mL were excluded from the analysis. For the 125 participants, median overall survival (OS) and recurrence-free survival were 23.1 and 12.1 months, respectively, with no significant differences between the study arms. Postresection CA19-9 levels and, to a lesser extent, CA19-9 change predicted OS (P = .040 and .077, respectively). For the 89 patients who completed the initial 3 cycles of adjuvant gemcitabine, the CA19-9 response was significantly correlated with initial failure over the distant site (P = .023) and OS (P = .0022). Despite a trend of less initial failure over the locoregional area (P = .031), neither postoperative CA19-9 level nor CA19-9 response helped to select patients who might have a survival benefit from additional adjuvant CRT. Conclusions: CA19-9 response to initial adjuvant gemcitabine predicts survival and distant failure of PDAC after resection; however, it cannot select patients suited for additional adjuvant CRT. Monitoring CA19-9 levels during adjuvant therapy for postoperative patients with PDAC may guide therapeutic decisions to prevent distant failure.