FISH probes improve detection of cholangiocarcinoma
Cholangiocarcinomas are a diverse group of biliary tract tumors characterized by epithelial differentiation. Depending on their location within the biliary tree, they are classified as intrahepatic, distal or perihilar. Although the three subtypes differ in progression, diagnosis and management, all cholangiocarcinomas have a poor prognosis — many are diagnosed late, and inoperable tumors are often resistant to chemotherapy and radiotherapy.
Perihilar cholangiocarcinoma (pCCA), which forms near the confluence of the left and right hepatic ducts, is the most common type of cholangiocarcinoma, and despite recent advances, it remains challenging to diagnose. Distinguishing malignant strictures from benign ones is difficult and can be further confounded by the presence of inflammation from primary sclerosing cholangitis — a stricturing disease of the bile ducts and established cholangiocarcinoma risk factor.
Conventional cytology vs. FISH
Endoscopic retrograde cholangiopancreatography (ERCP) is essential for assessing pancreatobiliary tract strictures; it allows visualization of the biliary tract, placement of biliary stents and collection of brushing cytology specimens. The detection of a dominant stricture or polypoid lesion by ERCP suggests the presence of pCCA and should be followed by cytological evaluation.
Conventional cytology has significant limitations, however, including sampling errors and a lack of cells in specimens, leading to sensitivity as low as 15 percent in some cases. As a result, other diagnostic techniques, including fluorescence in situ hybridization (FISH), have been studied to improve tumor detection.
FISH uses fluorescently labeled DNA probes to identify chromosomal aberrations in cells. Using these probes, researchers at Mayo Clinic's campus in Rochester, Minnesota, looked at multiple loci in archived biliary brushings to determine which had the highest sensitivity and specificity for biliary tract cancers. They identified four such loci: chromosomes 3, 7 and 17, and the chromosomal locus 9p21.
FISH using directly labeled DNA probes to the pericentromeric regions of these chromosomes has significantly improved sensitivity for the detection of biliary tract cancers compared with cytology alone, explains Gregory J. Gores, M.D., a specialist in hepatic cancer and cholangiocarcinoma at Mayo Clinic's campus in Rochester, Minnesota. FISH analyses that include probes to detect deletion of 9p21 increased diagnostic yield to 93 percent.
"We evaluate around 1,000 patients for cholanciocarcinoma each year. Those with strictures or jaundice have an 85 percent chance of having cancer, but with conventional techniques, you would only identify cancer in a small percentage of patients. With FISH, sensitivity is improved threefold. We have used a carefully validated new FISH probe set in clinical practice since the beginning of 2015, and so far the data hold up very well," he says.
Mayo Clinic has also developed tests to identify fusion genes in cholangiocarcinoma that may be important as driver mutations. Fusion genes are hybrid genes formed by linking two physically separate genes through insertions, deletions, inversions or translocations and are increasingly recognized as promising tools for the diagnosis and treatment of cancers. In cholangiocarcinoma, fibroblast growth factor receptor 2 (FGFR2) translocations may represent targets for tyrosine kinase inhibitor therapies.
A study published in Human Pathology in 2014 describes six patients with advanced cholangiocarcinoma, three of whom had recurrent translocations involving the FGFR2 locus. One patient with a FGFR2-TACC3 fusion was initially treated with pazopanib and later switched to the pan-FGFR inhibitor ponatinib, on which he has remained stable.
Based on these and other preliminary studies, Dr. Gores says Mayo is now beginning to group patients with cholangiocarcinoma into various genotypes that would allow for the use of more-targeted therapies.
For more information
Graham RP, et al. Fibroblast growth factor receptor 2 translocations in intrahepatic cholangiocarcinoma. Human Pathology. 2014;45:1630.