A post hoc analysis of the phase 3 PhALLCON trial reveals that ponatinib (Iclusig) demonstrates superior survival outcomes compared to imatinib (Gleevec) in patients with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) who remain positive for minimal residual disease (MRD) after induction therapy.
The analysis, presented at the 2025 EHA Congress, examined outcomes in patients who did not achieve MRD negativity by the end of induction and continued treatment beyond cycle 3. Among these patients, 56% in the ponatinib arm (86/154) failed to achieve MRD negativity compared with 69% in the imatinib arm (54/78).
Enhanced Molecular Response Rates
Of the 73 ponatinib-treated patients and 40 imatinib-treated patients who were MRD-positive after induction and continued treatment, 48% achieved MRD negativity by the end of treatment in the ponatinib arm versus 33% in the imatinib arm.
The analysis revealed progressive improvements in deep molecular responses with ponatinib. MR4 MRD negativity was achieved by 38% of ponatinib patients at the end of cycle 9, increasing to 41% at cycle 20 and 48% at treatment completion. In comparison, imatinib achieved MR4 rates of 28%, 30%, and 33% at these respective timepoints.
Even more striking were the MR4.5 MRD negativity rates, with ponatinib achieving 23%, 32%, and 37% at cycles 9, 20, and treatment end, respectively, compared to just 5%, 8%, and 10% for imatinib.
Significant Survival Benefits
The survival analysis demonstrated substantial clinical benefits for ponatinib in patients who remained MRD-positive after induction. The median event-free survival was not reached for ponatinib versus 24.8 months for imatinib (HR 0.198; 95% CI 0.075-0.527; P = 0.0004). Two-year event-free survival rates were 87% for ponatinib compared to 62% for imatinib.
Progression-free survival also favored ponatinib, with a median of 8.5 months versus 7.3 months for imatinib in MRD-positive patients (HR 0.569; P = 0.0207). The two-year progression-free survival rates were 36% and 13%, respectively.
Overall survival showed a trend toward improvement with ponatinib, though the median was not reached in either arm for MRD-positive patients (HR 0.277; P = 0.0468). Two-year overall survival rates were 91% for ponatinib versus 87% for imatinib.
Transplant Considerations
The analysis revealed that 29% of ponatinib patients who achieved MRD negativity after induction proceeded to hematopoietic stem cell transplant, compared with 46% of imatinib patients, suggesting that deeper molecular responses with ponatinib may reduce the need for transplantation.
Safety Profile
Treatment-emergent adverse events occurred in all ponatinib patients (100%) versus 98% of imatinib patients among those who did not achieve MRD negativity after induction. Grade 3 or higher adverse events were reported in 91% of ponatinib patients and 94% of imatinib patients.
Ponatinib led to dose interruptions in 66% of patients, dose reductions in 16%, and treatment discontinuation in 15%. The corresponding rates for imatinib were 41%, 28%, and 9%, respectively.
Treatment-emergent arterial occlusive events were rare, occurring in 3% of ponatinib patients versus 2% of imatinib patients at any grade, with grade 3 or higher events in 2% and 0%, respectively.
Clinical Implications
"These results appear to support the clinical benefit and tolerability of continuing ponatinib beyond cycle 3 in patients with newly diagnosed, Ph-positive ALL who have not achieved MRD negativity by the end of induction," stated lead study author Carlo Gambacorti-Passerini, MD, of the University of Milano-Bicocca in Monza, Italy.
However, Gambacorti-Passerini cautioned that this post hoc analysis should be interpreted carefully "due to the small number of patients and the potential for selection bias."
The PhALLCON trial originally demonstrated that ponatinib achieved a 30% MRD-negative complete remission rate at the end of induction compared to 12% for imatinib (difference 18%; P = 0.0004), leading to FDA accelerated approval of ponatinib in combination with chemotherapy for newly diagnosed Ph+ ALL in March 2024.
Ibrahim Aldoss, MD, associate professor at City of Hope, noted that while long-term follow-up data from PhALLCON are still maturing, the progression-free survival improvements with ponatinib are already evident, particularly in patients who fail to achieve early MRD negativity.
