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

We identified 243 patients with Ph-positive CML who had BCR-ABL transcripts monitored by quantitative RT-PCR after allogeneic stem cell transplant 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 three occasions or reached 0.05% on two occasions. Patients were allocated to one of four 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 one positive result but never more than two consecutive positive results; (3) 27 patients, 'persistently positive, low level', had persisting low levels of BCR-ABL transcripts but never more than three 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 transcript satisfied our definitions of MR whereas the majority of patients who did so were likely to progress further