MA26.06 Crizotinib-Treated ALK Immunopositive Metastasized NSCLC is Associated with an Unfavorable Prognosis when FISH Negative

Abstract

Background Metastasized NSCLC with an ALK fusion are sensitive to a range of tyrosine kinase inhibitors. ALK-positive NSCLC has been identified in the pivotal phase III trial with fluorescence in situ hybridization (ALK FISH+). These tumors are also expressing the fusion product (ALK immunohistochemistry (IHC)+). However, discrepant cases occur, including ALK IHC+ FISH-. The aim of this study was to collect ALK IHC+ cases and compare within this group response to crizotinib treatment of ALK FISH+ cases with ALK FISH- cases. Method A prospective multicenter investigator initiated research study was started in Europe. Stage IV ALK IHC+ NSCLC cases treated with crizotinib were collected centrally. Slides were validated centrally for ALK IHC (with 5A4 ETOP and D5F3 Ventana protocol) and ALK FISH (Vysis probes). Result The study started April 1, 2014 and closed in November 2017. Fifteen centers participated. Registration of 3523 ALK IHC tests revealed prevalence of 2.6% ALK IHC+ cases. Local ALK FISH analysis resulted in 46 concordant (ALK IHC+/FISH+) and 18 discordant (ALK IHC+/FISH-) cases. Central validation revealed 37 concordant and 6 discordant cases, 5 of which had follow-up. Validation was hampered by limited amount of tissue in biopsy samples. The time to treatment failure did not differ for concordant nor discordant cases, and neither for local nor validated ALK testing (HR=0.78; 95% CI= 0.27-2.3; p=0.64) and (HR=2.2; 95% CI= 0.72-6.5; p=0.16), respectively). However, overall survival was significantly better for concordant cases than discordant cases after central validation (HR=4.5; 95% CI= 1.2-15.9; p=0.010), but not according to local testing (HR=1.7; 95% CI= 0.45-6.2; p=0.44). Conclusion ALK IHC+ FISH- NSCLC cases are an infrequent finding. We recommend such cases to be validated carefully because our data indicate that ALK IHC+ FISH- cases have a worse survival when treated by crizotinib compared to ALK IHC+ FISH+ cases. This study was funded by an independent research grant by Pfizer.