Impact of frontline treatment approach on outcomes of myeloid blast phase CML

Background: The natural course of untreated chronic myeloid leukemia (CML) is progression to an aggressive blast phase. Even in the current era of BCR-ABL1 tyrosine kinase inhibitors (TKIs), the outcomes of blast phase CML remain poor with no consensus frontline treatment approach. Methods: We retrospectively analyzed the response rates and survival outcomes of 104 consecutive patients with myeloid blast phase CML (CML-MBP) treated from 2000 to 2019 based on 4 different frontline treatment approaches: intensive chemotherapy (IC) + TKI (n = 20), hypomethylating agent (HMA) + TKI (n = 20), TKI alone (n = 56), or IC alone (n = 8). We also evaluated the impact of TKI selection and subsequent allogeneic stem cell transplant (ASCT) on patient outcomes. Results: Response rates were similar between patients treated with IC + TKI and HMA + TKI. Compared to treatment with TKI alone, treatment with IC/HMA + TKI resulted in a higher rate of complete remission (CR) or CR with incomplete count recovery (CRi) (57.5% vs 33.9%, p < 0.05), a higher complete cytogenetic response rate (45% vs 10.7%, p < 0.001), and more patients proceeding to ASCT (32.5% vs 10.7%, p < 0.01). With a median follow-up of 6.7 years, long-term outcomes were similar between the IC + TKI and HMA + TKI groups. Combination therapy with IC/HMA + TKI was superior to therapy with TKI alone, including when analysis was limited to those treated with a 2nd/3rd-generation TKI. When using a 2nd/3rd-generation TKI, IC/HMA + TKI led to lower 5-year cumulative incidence of relapse (CIR; 44% vs 86%, p < 0.05) and superior 5-year event-free survival (EFS; 28% vs 0%, p < 0.05) and overall survival (OS; 34% vs 8%, p = 0.23) compared to TKI alone. Among patients who received IC/HMA + TKI, EFS and OS was superior for patients who received a 2nd/3rd generation TKI compared to those who received imatinib-based therapy. In a landmark analysis, 5-year OS was higher for patients who proceeded to ASCT (58% vs 22%, p = 0.12). Conclusions: Compared to patients treated with TKI alone for CML-MBP, treatment with IC + TKI or HMA + TKI led to improved response rates, CIR, EFS, and OS, particularly for patients who received a 2nd/3rd-generation TKI. Combination therapy with IC + TKI or HMA + TKI, rather than a TKI alone, should be considered the optimal treatment strategy for patients with CML-MBP.