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This thesis explores strategies to enhance deep molecular response (DMR) rates and treatment-free remission (TFR) eligibility in chronic myeloid leukaemia (CML), investigates factors linked to treatment milestone failures, describes tyrosine kinase inhibitor (TKI) discontinuation outcomes in a population-based cohort, and examines TFR probabilities after a second TKI discontinuation. In paper I we examined data from the Swedish CML registry on 128 CML patients in chronic phase with a reported TKI discontinuation of ≥1 month due to DMR. Findings indicate that patients discontinuing a 2nd generation TKI had a higher probability of remaining treatment-free, and 11% of patients with a diagnosis of CML in chronic phase were treatment free by last follow-up. Paper II involved a long-term follow-up of 40 patients treated initially with a 2nd generation TKI, dasatinib, combined with a low dose of pegylated interferon α2b as part of the phase II study NordCML007. The combination had an acceptable toxicity profile, and the occurrence of late dasatinib-related adverse events was not increased compared with previous studies of single treatment with dasatinib. The proportion of patients achieving major and DMR were high in comparison with historical cohorts of patients treated with dasatinib. In paper III, an interim analysis was conducted on CML patients attempting a second TKI discontinuation within the DAstop2 study, after a prior molecular relapse. After a median 27 months from the second discontinuation attempt, 50% had re-initiated TKI therapy, and TFR rate after 12 months was 56%. Those with a short (<6 months) TFR duration after the first discontinuation attempt were more likely to experience a molecular relapse after the second discontinuation attempt. Paper IV retrospectively analysed 20 patients newly diagnosed with CML in chronic phase and primary refractory to TKI treatment without BCR::ABL1 kinase domain mutations. Diagnostic samples were analysed for pathogenic variants in a panel of 54 genes recurrently mutated in myeloid neoplasms. Pathogenic variants were seen in 50% with AXL1 being the most frequently affected gene. All patients with truncating ASXL1 variants exhibited resistance to multiple TKIs. Overall, this thesis highlights the potential of TKI discontinuation in selected CML patients, the promising combination of dasatinib and pegylated interferon α in achieving high DMR rates, and the importance of genetic profiling in understanding TKI resistance.