Comparison of fluorescence in situ hybridization and cytology for the accurate detection of malignant biliary strictures, with emphasis on unusual results.

Introduction: Biliary brushing cytology is the standard diagnostic approach for evaluating biliary strictures, but it has low sensitivity and a high rate of atypical diagnoses. Fluorescence in situ hybridization (FISH) has become an increasingly valuable adjunct to cytology. Therefore, the aim of this retrospective quality improvement study was to evaluate the relative diagnostic performance of traditional cytology and FISH for correctly determining malignant versus benign biliary strictures from biliary brushing samples and to evaluate whether adding FISH to the diagnostic pipeline improves diagnostic accuracy over relying on cytology alone.

Materials and methods: We conducted a retrospective study of biliary brushing and FISH results in patients evaluated for biliary strictures between April 2019 and March 2023.

Results: A total of 228 specimens were retrieved. For cytology results: 151 negative, 55 atypical, 6 suspicious, and 16 positive. For FISH results: 105 negative, 71 equivocal, and 52 positive. When calculating performance measures, cytology atypical and FISH equivocal were excluded; cytology suspicious was considered positive. The sensitivity and specificity of cytology were 45.8% and 100%, respectively. The sensitivity and specificity of FISH were 84.2% and 96.0%, respectively.

Conclusions: Our findings indicate that FISH exhibits considerably higher diagnostic sensitivity than routine cytology in identifying malignant biliary strictures. Furthermore, combining cytology with FISH may provide a more comprehensive diagnostic approach, reducing the likelihood of false-negative results. However, positive and equivocal FISH results should be interpreted carefully and considered alongside more specific cytology findings to minimize the risk of false-positive diagnoses.