Microsatellite Instability Analysis and Its Prognostic Value in Invasive Nonampullary Duodenal Adenocarcinoma
Abstract Purpose: Nonampullary duodenal adenocarcinoma is a rare disease. Although several prognostic factors have been reported for this disease, they remain controversial due to their rarity. In this study, we retrospectively analyzed 54 cases of invasive nonampullary duodenal adenocarcinoma, focusing on the microsatellite instability phenotype, PD-L1 expression, and prognostic factors. Methods: Expression of the PD-L1 protein and cell differentiation markers in tumors was detected by immunohistochemistry. Microsatellite markers (NR-21, NR-22, NR-24, BAT-25 and BAT-26) were amplified for MSI assessment by PCR.Results: The incidence of microsatellite instability in invasive nonampullary duodenal adenocarcinoma was 35.2%. No significant correlation between the microsatellite instability phenotype and clinicopathological factors was observed. Positive expression of PD-L1 by immune cells was common in advanced-stage disease (P=0.054), and positive expression of PD-L1 in cancer cells correlated significantly with the histologically undifferentiated type (P=0.016). Kaplan-Meier survival analysis demonstrated a significantly better overall survival in patients with microsatellite instability (P=0.013) and at early-stage disease (P=0.000) than in those with microsatellite stability or at late tumor stages. Univariate and multivariate analyses showed that microsatellite instability (hazard ratio [HR]: 0.282, 95% confidence interval [CI]: 0.106-0.751, p=0.011) and early tumor stage (stage Ⅰ-Ⅱ) (hazard ratio [HR]: 8.81, 95% confidence interval [CI]: 2.545-30.500, p=0.001) were independent better prognostic factors of overall survival. Conclusions: Microsatellite instability and early tumor stage (stage Ⅰ-Ⅱ) were independent better prognostic factors of overall survival. A high proportion of microsatellite instability phenotypes and positive PD-L1 expression may be helpful for identifying immune checkpoint inhibitors as a novel therapeutic strategy.