Monitoring of minimal residual disease in patients with MLL-AF6-positive acute myeloid leukaemia by reverse transcriptase polymerase chain reaction

We studied 210 unselected patients with acute myeloid leukaemia (AML) for M LL abnormalities, Twenty-seven patients (13%) with rearranged MLL genes wer e identified by means of Southern blot analysis. An MLL-AF6 fusion transcri pt was detected in six patients by a reverse transcriptase polymerase chain reaction (RT-PCR) for the MLL-AF6 translocation. Sequence analysis showed fusion of MLL exon 7 as well as exon 6 (two patients) or MLL exon 6 as well as exon 5 (four patients) to AF6 exon 2. In only three patients could the t(6;11) also be identified by cytogenetic and/or fluorescence in situ hybri dization (FISH) analysis. The MLL-AF6-positive patients were monitored by R T-PCR for a period of 6-33 months, Complete haematological remission (CR) w as achieved in all six cases, but was short in 5/6 patients (range 2.6-8.3 months). In these five patients, the MLL-AF6 transcripts were detected in e very sample tested after induction and consolidation chemotherapy. One pati ent received autologous bone marrow transplantation (BMT) which also did no t lead to PCR negativity Intensive salvage therapy was unable to induce a s econd remission in the relapsed patients, One of the six MLL-AF6-positive p atients achieved a molecular CR. He is still in CR at 33 months after diagn osis. Survival analysis indicates a poor prognosis in MLL-AF6-positive pati ents. The median event-free survival was 6.8 months, the median overall sur vival 15 months. Persistent PCR positivity was consistently associated with relapse. Thus, RT-PCR provides a valuable and sensitive tool for the ident ification of t(6;11)-positive AML and the monitoring of response to treatme nt in these patients. The results of RT-PCR may be useful to evaluate thera peutic procedures and to make treatment decisions, which will enable molecu lar remissions to be achieved and improve the clinical outcome in this grou p of patients.