Pailler et al. investigated ALK-copy number gains (CNG) in individual CTCs by filter-adapted fluorescent in situ hybridization (FA-FISH) and reported a significant association between the dynamic evolution of the numbers of ALK-CNG and progression-free survival (PFS) in NSCLC patients treated with crizotinib, an ALK/ROS1 inhibitor 20. Here, ALK is linked to non-small cell lung carcinoma.