Background: Neoadjuvant therapy (NAT) is increasingly utilized for pancreatic cancer, however the added benefit of adjuvant therapy (AT) in this setting is unknown. We hypothesized that the magnitude of CA19-9 response to NAT can guide the need for further AT in resected pancreatic cancer. Methods: CA19-9 secretors who received NAT for pancreatic cancer during 2008–2016 at a single institution were analyzed and CA19-9 response (difference between pre- and post-NAT values) was measured. Kaplan–Meier estimators and Cox proportional hazard ratio models were used to determine the optimal CA19-9 response at which AT ceases to confer any additional survival benefit after NAT. Results: A total of 241 patients (mean age 65.4 years, 50% female) with complete CA19-9 data who underwent NAT followed by resection were analyzed. In a cohort of patients (n = 78) in whom CA19-9 normalized with a decrease > 50% after NAT (optimal responders), AT was not associated with additional survival benefit (40.6 vs. 39.0 months, p = 0.815). Conversely, in the cohort of patients (n = 163) in whom NAT was not associated with normalization and a decrease of ≤ 50% in CA19-9 (suboptimal responders), receipt of AT was associated with a survival benefit (34.5 vs. 19.1 months, p < 0.001) following NAT. A Cox proportional hazards model confirmed CA19-9 normalization and decrease > 50% during NAT to predict no additional survival benefit from AT. Conclusions: The magnitude of CA19-9 response to NAT may predict the need for further AT in resected pancreatic cancer. Prospective studies are needed to elucidate the optimal interplay of NAT and AT in pancreatic cancer.
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