Compound mutations involving T315I and P-loop mutations are the major components of multiple mutations detected in tyrosine kinase inhibitor resistant chronic myeloid leukemia.

To analyze the pattern of multiple mutations detected by Sanger sequencing (SS), we performed subcloning sequencing using 218 samples from 45 patients with tyrosine kinase inhibitor resistant chronic myeloid leukemia. At the first time of multiple mutation detection by SS (baseline), a total of 19 major mutations from 45 samples were detected; these mutations were found in the following order: T315I (68.9%), E255 K (33.3%), Y253H (13.3%), G250E (13.3%), and F317 L (11.1%). Subcloning sequencing of 900 baseline colonies identified 556 different mutant types, and 791 among the 900 were colonies with major mutations (87.9%). The mutations were found in the following order: T315I (36.4%), E255 K (16.2%), Y253H (7.0%), G250E (6.7%), M351 T (6.6%), and E255 V (5.3%). In subcloning sequencing with 4357 colonies of 218 serial samples, 2506 colonies (57.5%) had compound mutations, among which 2238 colonies (89.3%) had at least one major mutation. The median number of mutations in compound mutant colonies was 2 (range, 2-7), and most were double (52.9%) or triple (28.7%) mutations. Additionally, some mutations in allosteric binding sites were detected as low level mutation in 13 patients. With the available retrospective samples before baseline, subcloning sequencing identified low-level mutations of various frequencies (median, 10%) to be major mutations in 20 patients. Thus, compound mutations involving T315I and P-loop mutations were the major components of multiple mutations, and some low-level mutations with potential clinical significance were detected by subcloning sequencing. Hence, more sensitive sequencing assays are needed in patients with multiple mutations.

Baseline BCR-ABL1 transcript type of e13a2 and large spleen size are predictors of poor long-term outcomes in chronic phase chronic myeloid leukemia patients who failed to achieve an early molecular response after 3 months of imatinib therapy.

We conducted this study to identify the factors for predicting poor outcomes in chronic myeloid leukemia patients who failed to achieve a 3-month early molecular response (EMR). Of the 413 newly diagnosed, chronic phase, chronic myeloid leukemia patients receiving imatinib (IM), 120 (29.1%) failed to achieve a 3-month EMR. With a median follow-up of 67.0 months, 39 patients continued IM treatment with at least complete cytogenetic response (CCyR), and 81 patients permanently discontinued IM treatment. The cumulative incidence rates of CCyR and major molecular response (MMR) by 3 years were 90.1 ± 3.9% and 53.7 ± 7.3%, respectively. After adjusting for potential factors, multivariate analyses showed that a transcript type of e13a2, compared with e14a2, and a larger spleen size were independent factors for failure of overall MMR. The predictive factors outlined in this study may provide valuable information for high-risk patients who would benefit from early decision-making regarding therapy change.