The role of fluorescence in situ hybridization in primary diagnosis of distal biliary strictures

Summary: Background and aim: Primary diagnosis of the distal biliary stricture can be sometime difficult. Brush cytology (BC) is known to have low diagnostic sensitivity in these cases. Fluorescence in situ hybridization (FISH) has been reported as a useful adjunctive test in patients with biliary strictures. We aimed to determine performance characteristics of BC, FISH and their combination (BC + FISH) in the primary diagnosis of distal biliary strictures. Methods: This single-center prospective study was conducted between April 2019 and January 2021. Consecutive patients with unsampled biliary strictures undergoing first ERCP in our institution were included. Cytological and FISH analysis of tissue specimens from two standardized transpapillary brushings from the distal strictures were provided. Histopathological confirmation after surgery or 12-month follow-up was regarded as the reference standard for the final diagnosis. Results: A total of 109 patients were enrolled. Seven patients were lost from the final analysis and 26 suffered proximal stenosis. Of the 76 remaining patients (61.8% males, mean age 67.6, range 25–89 years) with distal stenosis, the proportions of benign and malignant strictures were 25 (32.9%) and 51 (67.1%), respectively. Of the subgroup of malignant strictures, 17.7% were cholangiocarcinoma, 74.5% were pancreatic tumors and 7.8% others. In comparison to BC alone, FISH increased the sensitivity from 0.373% to 0.706% (p = 0.0007) with a slight decrease in specificity (p = 0.045). Conclusions: Dual modality tissue evaluation using BC + FISH has better sensitivity for the primary diagnosis of distal biliary strictures, compared to BC alone. Key words: primary diagnosis of distal biliary strictures – first retrograde cholangiopancreatography – brush cytology – fluorescence in situ hybridization