Patients with primary sclerosing cholangitis (PSC) are at increased risk for developing cholangiocarcinoma (CCA). Fluorescence in situ hybridization (FISH) is a cytological test designed to enhance early CCA diagnosis. The long-term outcome of PSC patients with a positive FISH test (polysomy, trisomy/tetrasomy) are unclear. All PSC patients with at least one FISH test were identified and defined to have CCA if they had a positive tissue biopsy, positive cytology, or evidence of cancer in the explant after liver transplantation. A total of 235 PSC patients had at least one FISH test performed, and 56 patients had CCA on histopathology (n = 35) or cytology (n = 21). Overall, 120 of 235 (51%) of PSC patients tested for FISH were positive, but only one third of these positive patients had CCA. Sensitivity and specificity for FISH polysomy were 46% and 88%, and for trisomy/tetrasomy they were 25% and 67%, respectively. Survival analysis showed that patients with FISH polysomy had an outcome similar to patients with CCA; whereas FISH trisomy/tetrasomy patients had an outcome similar to patients with negative FISH tests. The FISH polysomy patients without cancer compared with those with CCA had lower serum bilirubin, lower carbohydrate antigen 19-9 (CA 19-9), lower Mayo risk score, and lower occurrence of dominant strictures. Conclusion: In PSC patients, the presence of a dominant stricture plus FISH polysomy has a specificity of 88% for CCA. Patients with FISH showing trisomy or tetrasomy have a similar outcome to patients with negative FISH. FISH testing should be used selectively in patients with other signs indicating CCA and not as a screening tool in all PSC patients undergoing endoscopic retrograde cholangiopancreatography (ERCP).
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