The pattern of mucin 5AC (MUC5AC) expression using immunohistochemistry and its prognostic significance in patients with pancreatic ductal adenocarcinoma.

Abstract

e16756 Background: Mucin-5AC (MUC5AC) is a secreted form of mucin. Its expression correlates with poor outcome in uterine, ampullary adenocarcinoma and cholangiocarcinoma. Its prognostic significance in pancreatic ductal adenocarcinoma (PDAC) is not well established. Here, we explored the pattern of MUC5AC expression using immunohistochemistry (IHC) and its prognostic significance in patients with PDAC. Methods: This is a retrospective study conducted at the University of South Alabama/Mitchell Cancer Institute. Between 2015-2019, 218 patients with PDAC were identified. Among this cohort, only 45 patients had tissue available for MUC5AC IHC staining. Two pathologists in- dependently scored the expression of MUC5AC. Staining percentage was estimated in 10% increments. Unpaired t test and log-rank Wilcoxon tests were used for statistical analysis. Results: In our cohort, the median age was 65 years (42-85). Males represented 55%. Caucasians, African Americans and other ethnicities (e.g. Asians) represented 71%, 25% and 4% respectively. Twenty patients (44%) had metastatic stage IV disease and 25 patients (56%) had non-metastatic disease. Positive cytoplasmic and apical MUC5AC expression by IHC was seen in 82% and 80% of patients respectively. The median apical MUC5AC expression was higher in metastatic patients compared to non-metastatic patients (67.5 % vs 30%, p = 0.0187 ) while there was no difference in the median cytoplasmic MUC5AC expression between metastatic and non-metastatic patients (13.7 % vs 12.5%, p = 0.3328). In non-metastatic patients, compared to patients with positive apical MUC5AC expression, no expression (0%) was associated with worse overall survival (OS) (43 vs 13 m, p = 0.0322). In metastatic PDAC, there was no difference in OS between patients with positive or no apical MUC5AC expression (18 vs 21 m, p = 0.781). Compared to patients with positive cytoplasmic MUC5AC expression, patients with no cytoplasmic MUC5AC expression (0%) had no difference in OS in both non-metastatic (40 vs 32 m, p = 0.986) and metastatic (36 vs 12.5 m, p = 0.487) patients. Conclusions: MUC5AC expression assessment using IHC is feasible in patients with PDAC. In our cohort, apical, but not cytoplasmic, MUC5AC expression was different between metastatic and non-metatstaic patients and showed prognostic significance in non-metastatic patients. To our knowledge, this is the first study to show prognostic significance of MUC5AC expression in patients with PDAC using IHC.