Diagnosis of pancreaticobiliary malignancy by detection of minichromosome maintenance protein 5 in bile aspirates

Abstract

Biliary brush cytology is the standard method of sampling a biliary stricture but has a low sensitivity for the detection of malignancy. We have previously shown that minichromosome maintenance (MCM) replication proteins (Mcm2-7) are markers of dysplasia and have utilised these novel biomarkers of growth for the diagnosis of cervical and bladder cancer. We aimed to determine if MCM proteins are dysregulated in malignant pancreaticobiliary disease and if levels in bile are a sensitive marker of malignancy. In 30 tissue specimens from patients with malignant/benign biliary strictures, we studied Mcm2 and -5 expression by immunohistochemistry. Bile samples were also collected prospectively at endoscopic retrograde cholangiopancreatography from 102 consecutive patients with biliary strictures of established (n=42) or indeterminate aetiology (n=60). Patients with indeterminate strictures also underwent brush cytology as part of standard practice. Bile sediment Mcm5 levels were analysed using an automated immunofluorometric assay. In benign biliary strictures, Mcm2 and -5 protein expression was confined to the basal epithelial proliferative compartment - in contrast to malignant strictures where expression was seen in all tissue layers. The percentage of nuclei positive for Mcm2 was higher in malignant tissue (median 76.5%, range 42-92%) than in benign tissue (median 5%, range 0-33%) (P<0.0005), with similar results for Mcm5. Minichromosome maintenance protein 5 levels in bile were significantly more sensitive than brush cytology (66 vs 20%; P=0.004) for the detection of malignancy in patients with an indeterminate stricture, with a comparable positive predictive value (97 vs 100%; P=ns). In this study, we demonstrate that Mcm5 in bile detected by a simple automated test is a more sensitive indicator of pancreaticobiliary malignancy than routine brush cytology.

Figure 1

Minichromosome maintenance protein 2 expression in benign and neoplastic pancreaticobiliary diseases. (A) Normal pancreas showing absence of Mcm2 expression. (B) Moderately to poorly differentiated pancreatic adenocarcinoma showing high levels of Mcm2 expression. Occasional viable Mcm2-negative cells are present. (C) Section of a benign hilar stricture showing occasional Mcm2-positive cells at the base of glands. (D) Moderately to poorly differentiated cholangiocarcinoma showing high levels of Mcm2 expression. Mcm2=minichromosome maintenance protein 2.

Figure 2

Immunohistochemistry for Mcm5 in the (A) colonic crypt and (B) ampulla. At the base of epithelium, nuclei of epithelial cells are positive for Mcm5 (dark brown) in contrast to surface of epithelium where cells do not express Mcm5. Mcm5=minichromosome maintenance protein 5.

Figure 3

Box-and-whisker plot of range 25th–75th percentile and median Mcm2 expression in benign and malignant biliary strictures. Mcm2=minichromosome maintenance protein 2.

Figure 4

Receiver operating characteristic curve of immunofluorometric Mcm5 test. The jagged curve (solid line) is the nonparametric ROC curve. The diagonal line is the reference line. Area under the curve is 80% (95% CI 70–91). Mcm5=minichromosome maintenance protein 5; ROC=receiver operating characteristic.