Incorporation of Microsatellite Instability and Tumor-Infiltrating Lymphocytes in Opisthorchis viverrini-Associated Cholangiocarcinoma: Predicting Patient Outcomes

Background: Cholangiocarcinoma (CCA) has the highest incidence in Northeastern Thailand, where patients generally present with late diagnosis and poor prognosis. Opisthorchis viverrini (OV) infection is the major cause of CCA, with oxidative stress driving DNA mutations and genetic instability. Microsatellite instability (MSI) is a predictive biomarker in several cancers. This study aimed to investigate MSI status and its association with clinicopathological features and survival of CCA patients. Methods: Tissue and serum samples were collected from 25 surgical CCA patients. MSI status and mismatch repair (MMR) proteins were evaluated using an MSI scanner and immunohistochemistry (IHC). Serum OV IgG was assessed by ELISA, while tumor-infiltrating lymphocytes (TILs) were evaluated by two pathologists. Associations of MSI with clinicopathological features, OV status, MMR, and survival were analyzed. Results: Among CCA patients, 66.7% were MSI-high and 33.3% were MSI-low. MSI-high significantly correlated with age < 57 years, intraductal growth pattern, OV positivity, and early-stage disease. Patients with MSI-high and high TILs showed markedly improved median survival compared to MSI-low with low TILs (94.0 vs. 16.8 and 3.0 months; HR = 6.82 and 14.10; p = 0.004 and 0.001). Incorporation of MSI and TILs remained an independent prognostic factor in multivariate analysis (p < 0.05). Conclusions: MSI-high is highly prevalent in OV-associated CCA and is associated with intraductal growth, OV infection, and early-stage disease. Combined MSI and TIL status may serve as an independent prognostic factor, warranting validation in larger cohorts.