Diagnostic pitfalls and the value of fluorescence in situ hybridization as an adjunct to cytologic evaluation of bile duct brushings in patients with primary sclerosing cholangitis

BACKGROUND: Primary sclerosing cholangitis (PSC) can present diagnostic difficulties on bile duct brushings as cytologic features mimicking adenocarcinoma may exist. This study evaluates the role of fluorescence in‐situ hybridization (FISH) as an adjunct to cytologic evaluation. METHODS: From January 1, 2020, through December 31, 2021, 308 bile duct brushings were processed of which 34 (11%) were malignant, 25 (8%) were suspicious, 36 (12%) were atypical, 204 (66%) were negative and 10 (3%) were nondiagnostic. Follow‐up biopsies/resections were performed in the 95 cases with diagnostic cytology (atypical/suspicious/malignant) of which 12 (13%) showed primary sclerosing cholangitis and form the basis of this study. Cytologic, histologic and FISH findings are presented and discussed. RESULTS: Of the 12 bile duct brushings 4 (34%) were positive/suspicious for adenocarcinoma and 8 (66%) showed atypical epithelial cells. FISH was positive in 2/4 positive/suspicious brushings and negative in the remaining 2 brushings. Histologic findings confirmed the FISH results. The cytologic features of the 2 false positive cases overlapped those of adenocarcinoma. Two of the 8 bile duct brushings with atypical epithelial cells were positive/suspicious for adenocarcinoma on FISH analysis; findings confirmed on histologic follow‐up. The remaining 8 patients underwent surveillance for the development of adenocarcinoma with repeat bile duct brushings, FISH analysis and biopsies, each of which has been negative to date. CONCLUSION: FISH, as an adjunct to the cytologic evaluation of bile duct brushings from patients with PSC, plays a role in improving diagnostic accuracy and serves as a surveillance tool for the potential development of adenocarcinoma.