Addressing unmet clinical needs: FISHing for bile duct cancer (2014)

Strictures of the extrahepatic bile ducts are a common occurrence in clinical practice. Although many of these strictures are caused by biliary tract adenocarcinoma, these strictures also may be nonmalignant. For example, immunoglobulin 4 (IgG4) disease of the biliary tree also causes biliary strictures mimicking biliary tract cancer and is equally difficult to diagnosis. Thus, the clinician is often left with a dilemma: is the biliary stricture malignant or nonmalignant, and should the biliary stricture be managed with surgery, presuming it is malignant, with corticosteroids for IgG4 disease, or with cautious observation? Unfortunately, adenocarcinomas of the biliary tree are highly desmoplastic tumors and, thus, are relatively acellular. They also display a tropism for bile growing along the bile duct instead of in a mass-like structure early in their presentation, so they often are not associated with mass lesions. The serum tumor marker cancer antigen 19-9 (CA 19-9) lacks both sensitivity and specificity. Thus, the cytologic observations obtained using brush cytology during endoscopic procedures are the usual way in which these strictures are diagnosed. Unfortunately, biliary cytology has a sensitivity of only 20% to 40% for the diagnosis of biliary tract malignancies. This is because of the paucicellular nature of the specimens, the subjective nature of cytology, and the technical obstacles in obtaining adequate samples for cytologic review. To overcome these deficiencies of conventional cytology, we use fluorescence in situ hybridization (FISH) for all cytologic examinations originating from the biliary tree as a routine part of our practice. This has proved to be extremely helpful in the management of these patients.1 FISH is performed using a current commercial kit (UroVysion probe set; Abbott Molecular Inc., Des Plaines, Ill) that contains labeled DNA probes to the pericentromeric regions of chromosomes 3, 7, and 17 and to the chromosomal band 9p21p. Essentially, there are 4 observations originating from the FISH analysis. A normal FISH would have 2 colors for each probe and is consistent with a benign diagnosis. Trisomy 7, representing 3 signals for chromosome 7, is frequently observed in inflammatory biliary strictures. Trisomy 7 alone in the absence of an elevated serum CA 19-9 value or mass lesion usually implies an inflammatory stricture rather than a malignant stricture. Tetrasomy is also observed when there are 4 signals for each probe and likely reflects high cell turnover with a compensatory mitotic rate. Therefore, in our experience, tetrasomy is seldom associated with biliary tract cancer. Conversely, polysomy, which reflects gains of 2 or more of the 4 probes in at least 5 cells, signifies chromosomal instability. The presence of polysomy in a new stricture of the biliary tree is highly suggestive of biliary tract cancer. Polysomy in this condition has a sensitivity of approximately 50% with a specificity of greater than 95% for biliary cancer. Thus, this approach virtually doubles the yield of conventional cytology while maintaining a high specificity. The more problematic patients are those with underlying biliary tract disease, such as primary sclerosing cholangitis. In these patients, the disease process itself causes inflammatory strictures, yet the patients are at high risk for developing cholangiocarcinoma. Therefore, it is critical to distinguish between inflammatory versus malignant strictures in patients who have dominant strictures in the setting of primary sclerosing cholangitis. In this setting, the interpretation of biliary tract cytology is even more problematic, and it is not unusual to obtain readings of atypical cells and/or even a cytologic interpretation of suspicious for cancer. In primary sclerosing cholangitis, the FISH study is enormously helpful in interpreting the results from conventional cytology. In patients who have suspicious cytology plus a positive FISH, clinicians have to be extremely concerned about underlying malignancy. Likewise, many patients present with an elevated CA 19-9 level but no mass lesions on cross-sectional imagining studies. Such patients frequently undergo endoscopic retrograde cholangiopancreatography (ERCP) with brushings of the biliary tract to obtain cytologic specimens. In this context, an elevated CA 19-9 level plus FISH polysomy is also extremely worrisome for adenocarcinoma.2 Some patients with primary sclerosing cholangitis undergo an ERCP for a variety of reasons, including diagnostic indications, and the cellular specimens obtained from endoscopic brush cytology during the course of the procedure may demonstrate polysomy. In these cases, we like to repeat the study at 3-month or 4-month intervals to confirm the results. Patients who have confirmed polysomy over time also are at high risk for the development of biliary tract cancer.3 A caveat is that high-grade dysplasia in primary sclerosing cholangitis can be associated with polysomy.4 However, the presence of high-grade dysplasia may warrant therapeutic intervention and, thus, the presence of polysomy is clinically helpful. In summary, the assessment of biliary tract strictures is difficult and requires a constellation of findings, including the patient context, cross-sectional imaging studies, and serum tumor markers. Conventional cytology often lacks sensitivity and specificity in this setting. FISH cytologic analysis greatly aids the clinician in helping to make diagnostic and management decisions. I consider biliary FISH studies to be essential for my practice. Indeed, in addressing unmet clinical needs, FISHing for bile duct cancer is the right strategy. These are examples of cells that were probed with fluorescent probes for a biliary fluorescence in situ hybridization (FISH) study. The bar on top of the cells describes the probes used for this study where the centromere enumeration probe (CEP) and locus-specific indicator (LSI) targets are specified. The cell on the left is normal or disomy with 2 signals per probe or color. The cell on the right illustrates polysomy (>2 signals for at least 2 probes or colors). Polysomy indicates genetic aberrations consistent with malignancy. No specific funding was disclosed. Dr. Gores has a patent pending for “Materials and Methods for Diagnosis, Prognosis, Monitoring of Recurrence and Assessment of Therapeutic/Prophylactic Treatment of Pancreaticobiliary Cancer Application by novel FISH probes.” Gregory J. Gores, MD, is Executive Dean for Research at the Mayo Clinic College of Medicine. He is a past President of the American Association for the Study of Liver Diseases and the International Liver Cancer Association. Because of the breadth and depth of his interests, he has served as an Associate Editor for Hepatology on 2 separate terms and once for Gastroenterology. He has coauthored more than 500 total publications, which have been cited over 25,000 times. His clinical and research contributions include advances in our understanding of hepatobiliary malignancies. He has coauthored several studies regarding the use of fluorescence in situ hybridization for the diagnosis of cholangiocarcinoma.