Schematic representation of the BCR-ABL1 mutation analyses performed in this study. BCR-ABL1 mutation analysis (Sanger sequencing [SS] and next-generation sequencing [NGS]) was conducted on baseline samples from all chronic-phase chronic myeloid leukemia (CP-CML) patients in the PACE phase 2 study. Postbaseline analysis (SS) was conducted on any patient who did not achieve major cytogenetic response (MCyR) by 1 year, achieved and then lost MCyR, or achieved MCyR and discontinued while in MCyR. *Postbaseline (post-BL) analysis was not conducted on patients who achieved MCyR and remain on study in continuous MCyR. ^36 patients were not evaluable: 12 did not have a post-BL sample collected, and BCR-ABL1 could not be amplified for sequencing in the remaining 24; 20 of these were associated with low (<1%) BCR-ABL1 transcript levels. Of the 129 patients with evaluable post-BL samples, 102 were collected from patients who did not achieve MCyR by 1 year, 14 from patients who achieved and lost MCyR, and 13 from patients who achieved MCyR and discontinued study while in MCyR.