Background: Development of cancer has been linked to inflammatory cytokines such as interleukin (IL)-6 and IL-17. In this study, we assessed the expression of these cytokines in intrahepatic cholangiocarcinoma (ICC) and determined their correlation to the survival probability. Methods: A total of 72 consecutive patients who underwent curative resection of ICC at Osaka University Hospital from March 1998 to November 2014 were enrolled. Immunohistochemical analysis was performed for IL-17 and its receptor A (IL-17RA), as well as IL-6. Enzyme-linked immunosorbent assay (ELISA) was performed for preoperative plasma levels of IL-6 and IL-17 in 32 patients with ICC. Results: Immunohistochemical analysis showed that the IL-6high (n = 34) and IL-17RAhigh (n = 29) groups had significantly worse disease-free survival (DFS) than IL-6low (n = 38) and IL-17RAlow (n = 43) groups, respectively. Although IL-17+ cells were abundant in the intratumoral area, patients with high peritumoral, but not intratumoral, IL-17+ cells (n = 28) corresponded with a significantly lower overall survival (OS) and DFS (OS, p = 0.023; DFS, p = 0.026) than those with low group. Moreover, multivariate Cox proportional hazards analysis revealed that IL-6, peritumoral IL-17+, and IL-17RA are independent prognostic factors for DFS (p = 0.023, p = 0.0088, p = 0.039, respectively). In addition, high preoperative plasma levels of IL-6 in patients with ICC corresponded with significantly lower DFS (p = 0.002). Conclusions: Our data suggested that IL-6, peritumoral IL-17+ cells, and IL-17RA expression are postoperative useful markers for predicting recurrence in patients with ICC.
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