Minimal residual disease after allogeneic bone marrow transplantation for chronic myeloid leukaemia in first chronic phase: correlations with acute graft-versus-host disease and relapse.

We have studied 61 patients who underwent allogeneic bone marrow transplantation (BMT) for chronic myeloid leukaemia (CML) in first chronic phase. Minimal residual disease was detected by the amplification of the leukaemia-specific BCR-ABL fusion mRNA with the polymerase chain reaction (PCR) using a highly sensitive nested primer strategy. As a general pattern, patients often had detectable BCR-ABL (PCR positive) for up to 6 or 9 months post BMT after which time BCR-ABL became undetectable (PCR negative). The conversion from PCR positive to PCR negative was not associated with the time at which cyclosporin A treatment was stopped. Six patients (10%) have relapsed during the period of this study, two within 1 year and four more than 1 year after transplant. The relationship between PCR positivity more than 1 year post transplant and relapse was significant (P = 0.036) but 15 patients who were PCR positive beyond 1 year remain in complete clinical and cytogenetic remission. Thus late positivity identifies a group of patients at increased risk of relapse but is of little predictive value for individual patients. Of the four late relapses, two had been persistently PCR positive and two were initially PCR positive, converted to negative and subsequently to positive again. Although all relapses were preceded by PCR positivity, relapse may occur only 12 months after a PCR negative result. The proportion of patients PCR negative at 3/4 months after BMT was found to increase significantly with the severity of acute GVHD (P = 0.002) but no relationship was found between acute GVHD and subsequent PCR results. There was no clear association between severity of chronic GVHD and PCR result.