Value of PCR analysis for long term survivors after allogeneic bone marrow transplant for chronic myelogenous leukemia: A comparative study

At present, allogeneic bone marrow transplantation (BMT) seems to be the only curative treatment for patients with chronic myeloid leukemia (CML). The mechanisms of this therapeutic approach probably include anti-leukemic immune response or ''graft-versus-leukemia'' (GVL) reaction against leukemic cell clones, since even aggressive chemotherapy is not sufficient per se to cure this type of disease. In many patients, allogeneic BMT results in the disappearance of the Ph chromosome; this negativity does not exclude the presence of residual leukemic cells since sensitivity of cytogenetic analysis is low. The chimeric BCR ABL gene in CML is a tumor-specific marker that is well suited to allowing detection of low numbers of residual leukemic cells through the extremely sensitive detection method of polymerase chain reaction (PCR). Using this method, 1 leukemic cell in 10(5) or 10(6) normal cells can be detected. Many studies have evaluated the clinical significance and predictive value of BCR-ABL gene rearrangement detected by PCR assay after BMT, most often on heterogeneous populations. Results from such studies have been conflicting. We have conducted a review of the literature, focussing on long-term survivors (>3 years from BMT) of CML to determine the value of PCR in such patients (n = 183). With the consideration that such a population is obviously heterogenous, long-term PCR negativity strongly correlated with achieving a cure since no patient relapsed in this population (n = 117). Among the PCR positive patients (n = 66), only 5 (8%) relapsed, suggesting a poor prognostic value for a PCR+ test >36 months post-transplant. Besides the potential clinical value of these data, they contribute to the understanding of the biology of the disease and may suggest a crucial role for the long term GVL effect of marrow transplantation.