We asked whether single circulating tumor cell (CTC) sequencing can inform on resistance mutations to ALK inhibitors and underlying tumor heterogeneity in ALK-rearranged NSCLC....Mutations were examined in CTCs from three patients (P41, P45, and P48) resistant to lorlatinib.At PD on lorlatinib, the patient underwent a tumor biopsy and was sampled for CTC analysis. ALKG1202R and ALKF1174L were detected with a VAF of 29% and 9% respectively in the tumor biopsy...CTC-10 harbored ALKG1202R/T1151M compound mutation with a VAF of 98% and 100% respectively...