Not Just Polysomy: Evaluating Non-Polysomy FISH Abnormalities In Diagnosis Of Malignancy In Biliary Strictures

Aims Fluorescence in situ hybridization (FISH) polysomy is known to be associated with malignancy in biliary strictures. However, interpreting genetic abnormalities other than polysomy, considered equivocal, remains complex. This study aims to assess the prevalence of malignancy associated with non-polysomy abnormalities using an optimized pancreatobiliary FISH (PB-FISH) assay [1].

Methods This study included patients undergoing endoscopic retrograde cholangiopancreatography (ERCP)-guided PB-FISH sampling for biliary strictures from October 2020 to February 2023. The PB-FISH results were interpreted according to the latest guidelines, assessing three specific genetic anomalies: 1) tetrasomy or trisomy without 9p21 deletion, 2) trisomy with 9p21 deletion, and 3) homozygous 9p21 deletion, both in patients with and without primary sclerosing cholangitis (PSC). False positive rate (FPR) and positive predictive value (PPV) of the aforementioned three thresholds were compared using the McNemar’s test. Analysis was conducted using R 4.1.3. (Table 1).

Results A total of 557 individuals (184 (33.1%) with PSC) with a mean age of 59.3 (standard deviation=16.7) were included. Malignancy was diagnosed in 178 (32.0%) individuals (71.9% cholangiocarcinoma). Non-polysomy abnormalities were noted in 61 (10.9%) individuals. For non-PSC patients, the highest FPR was observed in cases considered positive with tetrasomy/trisomy without 9p21 loss (6.1% [3.3-10.0%]). Conversely, cases with trisomy with 9p21 deletion had a significantly lower FPR (0.4% [0.1-2.4%]). All cases with homozygous loss of 9p21 were associated with malignancy. In PSC patients, PPVs were poor across all non-polysomy categories (Table 2), with a high risk of false positives noted: tetrasomy/trisomy without 9p21 deletion (90.4% FP), trisomy with 9p21 deletion (66.7% FP). Both PSC patients with homozygous 9p21 deletion were false positives.

Conclusions This study indicates that in patients without PSC, biliary strictures linked with trisomy and 9p21 deletion or homozygous loss of 9p21 strongly suggest malignancy, even without polysomy. Conversely, tetrasomy or trisomy without 9p21 deletion carries a high false positive risk and should not be the sole criterion for malignancy. In PSC patients, only polysomy should be considered a definitive positive due to the high false positive rate of other abnormalities. These insights can aid clinicians in more accurately interpreting PB-FISH results when polysomy is not the primary abnormality.

Publication History

Article published online:
27 March 2025

• References

• 1 Miller LJ, Holmes IM, Chen-Yost HI. et al. Performance of fluorescence in situ hybridization in biliary brushings with equivocal cytology: an institutional experience. Journal of the American Society of Cytopathology 2024; 13 (4): 285-290