Clinical and pathological significance of ROS1 expression in intrahepatic cholangiocarcinoma

Abstract

Background: More knowledge about genetic and molecular features of cholangiocarcinoma is needed to develop effective therapeutic strategies. We investigated the clinical and pathological significance of ROS1 expression in intrahepatic cholangiocarcinoma.

Methods: One hundred ninety-four patients with curatively resected intrahepatic cholangiocarcinoma were included in this study. Tumor tissue specimens were collected and analyzed for ROS1 gene rearrangement using fluorescence in situ hybridization (FISH) and ROS1 protein expression using immunohistochemistry (IHC).

Results: ROS1 immunohistochemistry was positive (moderate or strong staining) in 72 tumors (37.1 %). ROS1 protein expression was significantly correlated with well differentiated tumors, papillary or mucinous histology, oncocytic/hepatoid or intestinal type tumors, and periductal infiltrating or intraductal growing tumors (vs. mass-forming cholangiocarcinoma). ROS-expressing tumors were associated with better disease-free survival (30.1 months for ROS1 expression (+) tumors vs. 9.0 months for ROS1 (-) tumors, p = 0.006). Moreover, ROS1 expression was an independent predictor of better disease-free survival in a multivariate analysis (HR 0.607, 95 % CI 0.377-0.976; p = 0.039). Although break-apart FISH was successfully performed in 102 samples, a split pattern indicative of ROS1 gene rearrangement was not found in the examined samples.

Conclusion: ROS1 protein expression was associated with well-differentiated histology and better survival in our patients with resected intrahepatic cholangiocarcinoma. ROS1 gene rearrangement by break-apart FISH was not found in the examined samples.

Fig. 1

Selection of patients. This diagram summarized the selection of patients included in the study. Out of 555 patients who received liver resection for cholangiocarcinoma, 194 patients with curatively resected intrahepatic cholangiocarcinoma were included in the analysis

Fig. 2

​Immunohistochemical staining for ROS1. Tumor sections were stained for ROS1 with rabbit monoclonal antibody (D4D6), purchased from Cell Signaling Technology, Beverly, MA. The intensity of cytoplasmic staining was graded as (a) strong (3+); strong cytoplasmic staining with negative background staining, (b) moderate (2+); unequivocal positive staining with negative background staining, (c) weak (1+); faint staining in cytoplasm, or (d) negative; no staining in any cellular component. The photographs were taken at a magnification of x200

Fig. 3

Kaplan-Meier curves for disease-free survival and overall survival according to ROS1 expression. ROS-expressing tumors were associated with better disease-free survival (30.1 months for ROS1 expression (+) tumors vs. 9.0 months for ROS1 (−) tumors, p = 0.006). Also, patients with ROS1 (+) tumors had better overall survival, not reaching statistical significance (p = 0.071)