Addition of fluorescence in situ hybridization (FISH) and mutation analyses to cytology analysis significantly increases the sensitivity of detection of malignancies in biliary strictures, researchers report in the June issue of Clinical Gastroenterology and Hepatology.
These techniques can be performed using standard brush samples collected during endoscopic retrograde cholangiopancreatography, with mutations detected in free DNA in sample supernatants.
It is a challenge to detect malignancies in biliary strictures, even though many procedures and sampling techniques have been developed to evaluate strictures. Biliary brush samples for cytology analysis are typically obtained during endoscopic retrograde cholangiopancreatography (ERCP) or percutaneous transhepatic cholangiography.
Because cytology analysis identifies malignancies with nearly 100% specificity, a negative result rules out malignancy. However, cytology analysis of brush samples identifies maliganices with only 5% to 40% sensitivity, so it does not detect most most cancers.
FISH analysis of biliary samples can detect malignancies. FISH uses fluorescence-labeled probes to identify chromosomal abnormalities in cells obtained via routine biliary brushings. Polysomy of chromosomes 3, 7, and 17 centromeric regions or 1q21, 7p12, or 8q24 chromosomal regions are markers of malignancy, along with homozygous or heterozygous deletion of the 9p21 locus (p16).
PCR analysis of the DNA in residual fluid after centrifugation of cells from biliary brush specimens identifies cancer-associated mutations. PCR analysis of KRAS mutations and loss-of-heterozygosity in tumor suppressor genes (mutation analysis) has been reported to identify malignancies otherwise undetectable by cytology analysis.
Tamas A. Gonda et al compared the accuracies of cytology, FISH, and mutation analyses of biliary brush samples in detecting malignancy. They analyzed brush samples from 107 consecutive patients treated for biliary strictures by ERCP.
Gonda et al examined polysomy and p16 deletion using FISH analysis of biliary cells. They looked for KRAS mutations and loss of heterozygosity in tumor-suppressor genes using PCR-based analysis of free DNA in supernatant fluid from the same biliary brush samples.
As controls, strictures were determined to be nonmalignant based on repeat image analysis or laboratory test results 12 months after the procedure. Malignant strictures were identified based on subsequent biopsy or cytology analyses, pathology analyses of samples collected during surgery, or death from biliary malignancy.
Gonda et al found 41% of the patients in the final analysis to have biliary malignancies. Cytology analysis identified patients with malignancies with 32% sensitivity and 100% specificity. Addition of FISH or MP results to cytology results increased the sensitivity of detection to 51%, without reducing specificity. The combination of cytology, mutation analysis, and FISH analyses detected malignancies with 73% sensitivity.
FISH identified an additional 9 of the 28 malignancies not detected by cytology analysis, and mutation analysis identified an additional 8 malignancies. FISH and MP together identified 17 of the 28 malignancies not detected by cytology analysis.
Gonda et al concluded that addition of FISH and PCR mutation analysis can be used to rule out malignancy in brush samples with negative or indeterminate cytology results. They say that mutation analysis and FISH can be performed on specimens obtained in current clinical practice and do not require additional procedure time or expertise.
The authors noted that loss of heterozygosity in tumor suppressor genes alone detected malignancy in nearly half of all cases found to be positive by mutation analysis. Mutational analysis and FISH identified a non-overlapping set of 17 malignancies not detected by cytology.
One limitation of the study is that it included few patients with primary sclerosing cholangitis (PSC). PSCs have a high rate of aneuploidy so the specificity of FISH for detecting these cancers could be lower.
Additional studies are needed to determine the effects of combined tests in health economics.