Mutations were found in patients at the time of vemurafenib retreatment and 1 case of acquired resistance to vemurafenib. (A-C) Fishplot representation of sequencing data collected from patients at the time of vemurafenib treatment initiation and subsequent vemurafenib retreatment. Each patient had BRAFV600E mutation at the start of treatment that was suppressed during treatment and reappeared at the beginning of retreatment with the emergence of new subclones and/or persistence of prior subclones. (A) Patient ID1 had an initial complete hematologic response to vemurafenib retreatment but stopped responding during retreatment and was noted to have acquired a CDKN2A mutation at the time of resistance. Patient ID2 and Patient ID3 had acquired (B) HIST1H1D and PCBP1 mutations and (C) KEAP1 and NF1 mutations at the time of vemurafenib retreatment, but both patients achieved a complete hematologic response.