P1.02-045 Discordance (FISH+, IHC-) between FISH and IHC Analysis of ALK Status in Advanced Non-Small Cell Lung Cancer (NSCLC): A Unexpected Issue in 7 Cases: Topic: Driver Genes in NSCLC, Resistance, and Other

Anaplastic lymphoma kinase (ALK) rearrangement represents a landmark in the targeted therapy of NSCLC. Several reports showed that IHC is sensitive and specific to detect ALK protein expression, possibly alternative to ALK FISH assay. In this study the concordance between the ALK status by FISH and IHC assay has been determined in a series of 95 advanced NSCLCs; discordant cases were evaluated on the basis of the percentage and the rearrangement pattern of ALK. 95 lung NSCLC specimens were tested for ALK rearrangements by IHC assay (ALK D5F3 antibody Ventana, CE-IVD system) and by fluorescence in situ hybridization (FISH). Clinical characteristic and response to crizotinib were reviewed. Seven cases (7.3%) showed discordant results with ALK FISH-positive and IHC negative. Among these cases the mean number of FISH positive rearranged nuclei was 40.2% (range 20-54%). All cases showed coexistent split signals pattern positivity with mean percentage 19.1% (range 10-32%.), 5' deletions pattern positivity with mean percentage 21.7% (range 12-34%) and one case also had gene amplifications pattern positivity with percentage of 64%. The polysomy was observed in all cases with mean percentage of 45.7% (range of 16-72%). Five patients with discordant ALK FISH and IHC results received crizotinib; of them, four progressed and one has stable disease. In most of discordant cases, a coexistent complex pattern of rearrangements (deleted, inverted and amplified/polysomic patterns) of ALK positive cells in FISH analysis was observed; these complex rearranged cases were not detectable by IHC, probably due to the lack of protein expression. Considering that crizotinib inhibits the ALK protein and not specifically ALK rearrangements, it could be speculated that NSCLCs without IHC ALK expression could be not sensitive to crizotinib. The ALK FISH+/IHC negative discordant group showed a lower percentage of nuclei positive for ALK rearrangement (19.1% in split signals and 21.7% in 5' deletions) as compared with 64% of gene amplification in one case and with polysomy (45.7%) observed in all cases. These preliminary data highlight the role of IHC analysis and of the percentage of the genetic pattern of ALK rearranged cells in FISH analysis to select patients for anti ALK treatment. Further investigation is suggested about the correlation of complex mutational findings and clinical outcome.