Diagnostic implication of extracellular mucin in pancreatic/biliary brushing and stent cytology

Background Pancreatic and/or biliary (PB) brushing is commonly used to rule out malignant strictures. Many studies have attempted to characterize cytomorphologic characteristics of brushing and stent cytology. However, scant literature exists on the diagnostic implication (DI) of thick extracellular mucin (ECM) indicative of neoplasm in these samples. This study was aimed at reviewing the DI of thick ECM in PB brushing and stent cytology. Methods A retrospective search of consecutive cytologic samples of PB brushings/stents with corresponding surgical pathology or relevant clinical information over a 1‐year period was performed. Blinded review of the slides was performed by two cytopathologists. The slides were assessed for the presence, quantity, and quality of ECM. The results were analyzed for statistical significance with the Fisher exact and χ2 tests. Results One hundred ten cases were identified from 63 patients. Twenty‐two cases (20%) were PB brushings only without a prior stent. The remaining 88 cases (80%) had a preexisting stent for symptomatic obstruction. Fourteen of 22 cases (63%) without prior stents and 67 of 88 poststented cases (76%) were nonneoplastic (NN) upon follow‐up. ECM was present more frequently in neoplastic cases than in NN cases (p = .03). Among NN cases (n = 87), poststented samples showed more evidence of ECM than prestented samples (15% vs. 45%, p = .045). Identical thick ECM was observed in NN poststent and main‐duct intraductal papillary neoplasm samples. Conclusions Although ECM was frequently seen in neoplastic cases, NN cases showed increased evidence of thick ECM among poststented samples. Thick ECM may be common in stent cytology, regardless of the underlying biologic process. Extracellular mucin is frequently encountered in stent and poststent brushing cytology. Thick extracellular mucin may not be a useful diagnostic feature of neoplasm in stent cytology.