Post-transplant TKIs for Ph+ ALL: practices to date and clinical significance.

Post-transplant tyrosine kinase inhibitors (TKIs) show promise in preventing relapse after allogeneic hematopoietic cell transplantation (allo-HCT) for Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL). However, their real-world use and efficacy remain unclear. A comprehensive study across seven centers included Ph+ALL patients who underwent allo-HCT between 2002 and 2022. Post-transplant TKIs were administered in 28% of patients (49 of 173 transplanted in complete remission): 7% as prophylaxis during complete molecular remission (CMR), and 21% in response to measurable residual disease (MRD) positivity. Median first post-transplant TKI duration was 13.7 months for the prophylactic group and 4.0 months for the MRD-triggered group. Prophylactic TKIs appear particularly beneficial for patients not in CMR at allo-HCT, showing a trend towards higher 5-year relapse-free survival (RFS) compared to those not receiving prophylactic TKIs (100% vs. 73%; P = 0.11). Significant RFS differences were observed between the prophylactic, non-TKI, and MRD-triggered groups. However, patients with white blood cell counts <15000/µl at diagnosis and no additional chromosomal abnormalities-an MRD-triggered high efficacy cluster-demonstrated comparable 5-year RFS regardless of TKI strategy (100% vs. 85% vs. 80%; P = 0.87). This cluster highlights the potential effectiveness of MRD-triggered TKI administration in select low-risk patients, suggesting tailored TKI strategies based on risk factors.