Extracellular (EC) Mucin5AC (MUC5AC) detection after neoadjuvant therapy (NAT) and the risk of recurrence in resected pancreatic ductal adenocarcinoma (R-PDA).

4171 Background: The clinical significance of MUC5AC glycoforms is unclear to date. Our earlier study showed the association of lower mature (MM) and immature (IM) MUC5AC in R-PDA with pathological treatment response and EC detection of MM (EC-MM). Here, we have the significance of EC-MM detection in the tissue of R-PDA post-NAT. Methods: Formalin-fixed paraffin-embedded tissue blocks of R-PDA from January 2010 to June 2021 were obtained from the Ohio State University biorepository. Using monoclonal antibodies for 45M1 (MM) and CLH2 (IM), immunohistochemistry was performed to study the cellular expression of MM and IM, and H-scores were calculated. Also, the presence or absence of EC expression of MM is noted. progression-free survival (PFS) and overall survival (OS) were the primary endpoints. Univariate and multivariate Cox regression models were used to model PFS and OS, and clinical and pathological variables were adjusted in the multivariate models. We performed univariate logistic regression analysis to examine the impact of MUC5AC expression on pathological features in resected specimens. Results: Among 100 R-PDA patients, 43 received NAT and 57 had upfront surgery (UpS)). In NAT-group (36-FOLFIRINOX, 2-FOLFOX, and 5-gemcitabine/nab-paclitaxel), EC-MM detection in the resected specimens was associated with worse PFS on multivariate analysis (MVA) (Hazard Ratio (HR) 0.2, 95 % CI: 0.059-0.766, p = 0.01). In the FOLFIRINOX-treated group, the EC-MM detection had a similar impact (HR 0.2, 95 % CI: 0.052-0.847, p = 0.02) on PFS. Cellular MM and IM expression were significant (p < 0.05) on MVA for OS in both groups, but the HRs were not clinically significant (NAT-group, MM - 0.9 & IM - 1.04, FOLFIRNIOX-group, MM - 0.8 & IM -1.02). Expression levels of cellular MM and IM in FOLFIRINOX group and MM alone in NAT-group significantly (p < 0.05) correlated with incomplete resection (R1/R2 vs R0) and perineural invasion. In the UpS group, MUC5AC glycoforms did not significantly correlate with survival or pathological features. Conclusions: Post NAT EC-MM detection and cellular MUC5AC (MM and IM) expression levels are associated with worse PFS and pathological features. Their role in the treatment of naïve patients is still unclear. MUC5AC can be a clinically useful predictive biomarker. Future research should focus examining its importance in advanced tumors and manipulating it for therapeutic purposes.