Time to CA19-9 nadir: a clue for defining optimal treatment duration in patients with resectable pancreatic ductal adenocarcinoma

Background: Defining optimal treatment duration in patients with resectable pancreatic ductal adenocarcinoma (PDAC) receiving primary chemotherapy is an unmet need. The role of time to CA19-9 nadir and of nadir magnitude was explored in this study. Patients and methods: The databases of our institution’s prospective trials were queried to speculate on the time to maximum chemotherapy response. Patients with pathologically proven, metastatic (N = 356) or non-metastatic non-resected (N = 163) PDAC and elevated baseline (> 34 UI/mL) CA19-9 were analyzed. Survival curves were estimated using the Kaplan–Meier method and compared by means of the log-rank test for analyses including at least 45 patients. Multivariable Cox proportional hazards model was used to estimate clinical features for their association with OS. All probability values were from two-sided tests. Results: Time to CA19-9 nadir was ≥ 4 months in 184 of 346 (53%) metastatic and 121 of 163 (74%) non-metastatic patients (p = 0.002). The likelihood of a later nadir was higher with taxane-based chemotherapy as compared to taxane-free combinations (73% versus 56%; p = 0.02). Both metastatic and non-metastatic patients had significantly longer survival when nadir occurred later. Patients with a larger CA19-9 nadir magnitude had significantly longer survival. Metastatic patients with CA19-9 reduced by < 50%, 50–89%, or > 89% and had a median survival of 7.4, 9.8, and 14.7 months, respectively (p ≤ 0.001 for all comparisons). The corresponding figures for non-metastatic patients were 10.6; 17.0; and 18.7 months, respectively (p ≤ 0.02 for < 50% versus 50–89% or > 89%; p = 0.14 for 50–89% versus > 89%). Multivariable analyses showed that time to CA19-9 nadir but not CA19-9 nadir magnitude was independently predictive of survival. Conclusion: The present study suggests that a 4–6 months program might be a more suitable candidate for prospective assessment in comparison to shorter pre-defined period in patients who are candidates to surgery after primary chemotherapy.