Background: Biomarker testing in lung cancer is often limited by a lack of sufficient formalin fixed, paraffin embedded (FFPE) tissue for comprehensive genomic profiling. To promote personalized therapy for lung cancer, a multiplex FISH assay was developed to simultaneously assess aberrations in ROS1, RET, and MET on a single FFPE specimen slide.

Methods: Specimens included primary tumor (N = 39) as well as biopsies from a variety of metastatic sites (N = 16). These included 12 samples with ROS1 rearrangements, 3 samples with RET rearrangements, and 11 samples with MET amplification reported by a previously validated laboratory test method. A probe mix contained 6 differentially labeled fluorescent probes: 3' ROS1, 5' ROS1, 3' RET, 5' RET, MET and CEP7. The probes were formulated in Vysis IntelliFISH Hybridization Buffer to allow for a 2 h hybridization time. BioView imaging platform and Duet software algorithm were used to perform automated slide scanning and digital analysis. Specimens were considered positive for ROS1 or RET rearrangement if >15% evaluated cells contained a break apart (rearranged) signal. Specimens were considered positive for MET amplification if >15% of cells had MET/CEP7 ratio >2 and positive for polysomy if >15% of cells had 5 or more MET signals copies.

Results: The 6 color FISH assay was 97% concordant for ROS1 rearrangement and 100% concordant for RET rearrangement. The average background percentage of positive tumor cells in cases without known gene rearrangements was approximately 5%, yielding a negative cutoff threshold of approximately 15%, in accordance with cutoff thresholds reported in literature. The 6 color FISH assay was 91% concordant for MET amplification or polysomy. Results were interpretable for 98% of targets analyzed by the 6 color FISH method. Four samples failed on analysis for one of the targets due to lack of sufficient cells or lack of adequate hybridization signal.

Conclusion: A newly developed 6-color FISH assay allows simultaneous detection of three genomic abnormalities using only 1 specimen slide. This feature combined with rapid hybridization in IntelliFISH buffer and automated BioView slide imaging and analysis can significantly increase the yield of molecular testing on limited lung cancer tissue samples. Careful pathologic correlation for tumor cell identification and careful assessment of hybridization quality are necessary to optimize the accuracy of this test method.

Citation Format: Irina A. Sokolova, Patrick Bedroske, Tatyana A. Grushko, Amber R. Schneider, Kristine Jacobson, Jesse S. Voss, Yishay Tauber, Yossi Avisror, Vitaliy Shkolnik, Katerina Pestova, Katherine B. Geiersbach. Multiplex fast FISH assay for detecting ROS1, RET and MET aberrations in FFPE specimens using BioView image analysis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4256.