FISH Testing for Gallbladder Cancer
FISH (fluorescence in situ hybridization) is not used for diagnosing primary gallbladder cancer; it is specifically utilized for detecting cholangiocarcinoma (bile duct cancer) through biliary brush cytology obtained during ERCP, not for gallbladder malignancies.
Understanding FISH in Biliary Tract Malignancies
FISH testing uses DNA probes to identify chromosomal abnormalities such as aneuploidy and polysomy in biliary strictures 1. However, this technique is applied exclusively to cholangiocarcinoma (bile duct cancer), not gallbladder cancer 1.
Performance Characteristics for Cholangiocarcinoma (Not Gallbladder Cancer)
- Sensitivity: 64-68% for detecting cholangiocarcinoma 1
- Specificity: 70-94% for cholangiocarcinoma 1
- FISH enhances the diagnostic yield when combined with standard brush cytology during ERCP 1
When FISH is Recommended
FISH should be performed during ERCP evaluation of:
- Dominant biliary strictures in patients with primary sclerosing cholangitis 1
- Indeterminate biliary strictures suspicious for cholangiocarcinoma 1
- Patients with increasing CA19-9 levels and biliary abnormalities 1
FISH is NOT indicated for gallbladder masses or gallbladder wall thickening 1.
Diagnostic Approach for Gallbladder Cancer
For suspected gallbladder cancer, the appropriate diagnostic pathway includes:
Initial Imaging
- Transabdominal ultrasound as first-line investigation 2
- High-quality cross-sectional imaging (CT or MRI/MRCP) to evaluate gallbladder wall, detect tumor invasion, determine vascular involvement, and assess for metastases 1, 2
Tissue Diagnosis
- Pathological examination through fine needle aspiration, biopsy, or surgical specimen 1
- Final pathological diagnosis must be obtained before chemotherapy or radiotherapy 1
- Routine pathological examination of all cholecystectomy specimens is essential, as 47% of gallbladder cancers are discovered incidentally 3
Laboratory Markers
- CA19-9 and CEA may be measured but are not specific for gallbladder cancer 1, 2
- These markers cannot distinguish between gallbladder, pancreatic, or gastric malignancy 1
Critical Pitfalls to Avoid
- Do not request FISH testing for gallbladder masses—this test is only validated for biliary strictures and cholangiocarcinoma, not gallbladder cancer 1
- Do not rely on imaging alone for diagnosis; tissue confirmation is mandatory before initiating non-surgical oncological therapy 1
- Do not delay surgical evaluation in patients with suspicious gallbladder findings, as surgery is the only curative modality 3, 4
- Ensure all cholecystectomy specimens undergo pathological examination, as incidental gallbladder cancer occurs in 0.4-1.5% of cases and 74% require re-resection 3