Background: We explored the potential value of serum MUC5AC (sMUC5AC) as a biomarker to guide perioperative management of early-stage pancreatic ductal adenocarcinoma (PDA) patients receiving neoadjuvant therapy (NAT). Methods: We performed enzyme-linked immunoassays using a human MUC5AC kit (NBP2-76703) in serum samples obtained from The Ohio State University biorepository (between January 2010 and June 2021). Univariate (UV) and multivariate (MV) Cox regression models were used to quantify progression-free survival (PFS); clinical and pathological variables were adjusted in the MV models. UV logistic regression analysis was utilized to examine the association of sMUC5AC with pathological features and survival. 2 Results: Overall, 23 samples (19 FOLFIRINOX, 3 gemcitabine/nab-paclitaxel, 1 FOLFOX) were available for analysis. The median age was 66 years, and 52% were females. sMUC5AC was associated with a) treatment response, margin status, and residual disease (R0 vs. R1/R2) (all P<0.05); b) PFS on both UV (hazard ratio (HR) of 1.4, 95% confidence interval (CI) of 1.07 to 1.82, P=0.01) and MV (HR of 49.2, 95% CI, 4.4 to 1008.3, P=0.002) analyses; and c) PFS in pre-surgery models along with carbohydrate antigen 19-9 (CA19-9) measured on the same day alone (HR of 1.47, 95% CI, 1.06 to 1.93, p=0.04), with CA19-9 on the same day, and NAT regimen (HR of 1.44, 95% CI, 1.12 to 1.93, p=0.01), and with CA19-9 on the same day, NAT regimen, and CA19-9 at diagnosis (HR of 1.52, 95% CI, 1.1 to 2.09, p=0.007). Conclusion: sMUC5AC shows promise to helping to predict outcomes in our preliminary study. Larger prospective studies should validate these findings.