Optimal Value of CA19-9 Determined by KRAS-Mutated Circulating Tumor DNA Contributes to the Prediction of Prognosis in Pancreatic Cancer Patients

Despite the acceptance of carbohydrate antigen 19-9 (CA19-9) as a valuable predictor for the prognosis of pancreatic ductal adenocarcinoma (PDAC), controversy remains with regards to its cutoff. Our previous study showed a significant correlation between CA19-9 levels and the presence of KRAS -mutated ctDNA in the blood of patients with PDAC. Based on this correlation, we investigated the optimal cutoff value of CA19-9 before surgery. Continuous CA19-9 values and KRAS -mutated ctDNAs were monitored in 22 patients with unresectable PDAC who underwent chemotherapy between 2015 and 2017. Receiver operating characteristic curve analysis identified 949.7 U/mL of CA19-9 as the cutoff value corresponding to the presence of KRAS -mutated ctDNA. The median value of CA19-9 was 221.1 U/mL. These values were then verified for their prognostic values of recurrence-free survival (RFS) and overall survival (OS) in 60 patients who underwent surgery between 2005 and 2013. Multivariate analysis revealed that 949.7 U/mL of CA19-9 was an independent risk factor for OS and RFS in these patients (P=0.001 and P=0.010, respectively), along with lymph node metastasis (P=0.008 and P=0.017), but the median CA19-9 level was not (P=0.150 and P=0.210). The optimal CA19-9 level contributes to the prediction of prognosis in patients with PDAC before surgery.