Serial measurement of BCR-ABL transcripts in the peripheral blood after allogeneic stem cell transplantation for chronic myeloid leukemia: an attempt to define patients who may not require further therapy.

We identified 243 patients with Philadelphia (Ph) chromosome-positive chronic myeloid leukemia (CML) who had BCR-ABL transcripts monitored by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) after allogeneic stem cell transplantation for a median of 84.3 months. Individual patients were regarded as having achieved molecular relapse (MR) if the BCR-ABL/ABL ratio exceeded 0.02% on 3 occasions or reached 0.05% on 2 occasions. Patients were allocated to 1 of 4 categories: (1) 36 patients were "persistently negative" or had a single low-level positive result; (2) 51 patients, "fluctuating positive, low level," had more than 1 positive result but never more than 2 consecutive positive results; (3) 27 patients, "persistently positive, low level," had persisting low levels of BCR-ABL transcripts but never more than 3 consecutive positive results; and (4) 129 patients relapsed. In 107 of these, relapse was based initially only on molecular criteria; in 72 (67.3%) patients the leukemia progressed to cytogenetic or hematologic relapse either prior to or during treatment with donor lymphocyte infusions. We conclude that the pattern of BCR-ABL transcript levels after allograft is variable; only a minority of patients with fluctuating or persistent low levels of BCR-ABL transcripts satisfied our definitions of MR, whereas the majority of patients who did so were likely to progress further.