Background: Treatment for patients with chronic myeloid leukemia (CML) had a benchmark with the introduction of imatinib, a tyrosine kinase inhibitor (TKI). Nevertheless, resistance due to genetic mutations in the BCR::ABL1 kinase receptor remains relatively common for many patients, leading to failure, lack of response, or suboptimal response. Ideally, to bypass genetic resistance, guidelines recommend switching to a second-generation TKI, but for many developing countries, socioeconomic barriers hinder the possibility of switching medication. Despite this scenario, scarce information is available to evaluate the clinical prognosis of these patients. Methods: We conducted a retrospective cohort analysis to compare the overall mortality of patients with CML who developed a suboptimal response to standard-dose imatinib and were treated with either high-dose imatinib or a second-generation TKI. We created a marginal structural model with inverse probability weighting and stabilized weights and depicted the survival curves and median using the Kaplan-Meier estimator. Our primary outcome was overall survival (OS) at 150 months, defined as the number of deaths once patients had reached treatment response based on parameters of the European Leukemia Net Guidelines for CML. Our secondary outcomes were disease-free survival (DFS) at 150 months, defined as the number of months after patients achieved either major molecular response or deep molecular response, and adverse events that included gastrointestinal, dermatologic, hematologic, and others. Results: The cohort included 148 patients, of which 32 received high-dose imatinib and 116 a second-generation TKI. While we found no difference in the 150-month risk in both OS and DFS (Table), patients receiving second-generation TKI had an increase in median survival of OS (p-value = 0.009). No difference was found in the median survival of DFS (p-value = 0.55). No difference was found in either hematologic, gastrointestinal, dermatologic, or other adverse events (p-values of 0.39, 0.94, 0.24, and 0.33, respectively). Conclusions: Ideally, patients who develop a suboptimal response to imatinib should be switched to a second-generation TKI. However, If impossible, our findings suggest that patients treated with high-dose imatinib have a similar OS and DFS prognosis to those receiving a second-generation TKI.