RT-PCR studies in patients with chronic myeloid leukemia (CML) in remission 5 years after allogeneic stem cell transplant (SCT) define risk of subsequent relapse

103 consecutive patients in molecular remission 5 years after allogeneic SCT for CML with either HLA-identical sibling donors (n=71 ) or phenotypically HLA-matched unrelated donors (n=32) were identified. The study cohort was defined on the basis of survival with a negative RT-PCR for BCR-ABL transcripts in peripheral blood within 3 months of the 5 year landmark. The patients were classified into three groups: group A comprised 64 patients who had been continuously PCR negative post-transplant, group B 19 patients who had had one or more positive PCR study and group C 20 patients who had relapsed and had then regained complete molecular remission following treatment with donor lymphocyte infusion (DLI) within the initial 5 year period. All patients were monitored at regular intervals after the 5 year landmark. The median period of follow-up for all 103 patients was 8.4 yrs post-SCT (range 5-17.6 yrs). Of patients in group A. only one patient satisfied criteria for molecular relapse at 9.5 years and the actuarial survival at 10 years was 100%. 7 patients (37%) in group B satisfied molecular criteria for relapse and one of these proceeded to cytogenetic relapse. The actuarial survival at 10 years for group B patients was 90% and for group C patients was 100%. The probability of relapse at 10 years in group B patients was 54%. We conclude that molecular studies during the first 10 years post-transplant help to predict long-term leukemia-free survival and possibly cure of CML. Patients who show transient evidence of relapse at the molecular level within 5 years of SCT may be at a risk for subsequent sustained relapse. It is noteworthy that the significant minority who do relapse at a molecular level can be successfully restored to a molecular remission following treatment with DLI.