Curie FISH Analysis
FISH analysis was carried out on formalin-fixed, paraffin-embedded tissue sections with a break-apart probe specific to the ROS1 (Kreatech™ FISH probes ROS1 (6q22) Break – XL for BOND, Leica Biosystems) and the ALK (Kreatech™ FISH probes ALK (2p23) Break – XL for BOND, Leica Biosystems) loci according to the manufacturer’s instructions. The nuclei are stained using DAPI. Tumor cells, the nuclei of which had one or more FISH signals, were enumerated. The rearrangement-positive cells were defined as those with split signals or isolated signals. The PDX is considered as ROS1 or ALK -rearranged if more than 15% of the enumerated tumor cells showed probe signals.