Negative for Intraepithelial Lesion/Malignancy (NILM) Pap Slides from Women ≥ 30 Years of Age with Positive High-Risk HPV DNA: Focused Rescreening Prior to Report Issuance, an Enhanced Quality Control Measure

Abstract

Introduction: Fluorescence in situ hybridization (FISH) testing has a published sensitivity and specificity of 35% and 91%, respectively for the detection of biliary tract malignancy. In 2012, our institution experienced a false negative rate of 44% (70/160). The goal of this study was to identify the root causes of false negative FISH results in patients with biliary tract malignancy. Materials and Methods: Biliary brushings were collected and analyzed utilizing the UroVysion(TM) (Abbott Molecular, Des Plaines, IL) probe set. Cases with non-polysomy FISH result and clinicopathologic evidence of malignancy were identified. Malignancy was defined as a mass on imaging, positive biopsy or routine cytology result. A retrospective review of the FISH slide was performed by an experienced FISH technologist. FISH slides were evaluated for cellularity, hybridization quality, presence of obscuring material, and presence of polysomic cells (cells with gains of 2 more probes). Results: There were 70 false negative biliary brushings in 2012 from 49 unique patients. Cellularity and hybridization quality were suboptimal in 17% and 27% of specimens, respectively (Table 1). Fifty-seven percent contained obscuring material. One to four polysomic cells (cut-off for polysomy at our institution is 5 cells) were identified in 40% of specimens. None of the specimens fit the criteria for a positive FISH test on retrospective review. Twentysix percent of specimens had multiple limiting factors identified. Conclusions: Poor specimen quality and inadequate sampling, not test interpretation, were the root causes of false negative FISH results in patients with biliary tract malignancy at our institution, using the UroVysion(TM) probe set. Polysomy, due to chromosome abnormality not recognized by the UroVysion(TM) probe set, may also contribute to false negative cases, but was not assessed in this study.