Value of molecular monitoring during the treatment of chronic myeloid leukemia: A Cancer and Leukemia Group B study

Purpose: Disappearance of the Philadelphia chromosome during treatment for chronic myeloid leukemia (CML) has become on important therapeutic end point, To determine the additional value of molecular monitoring during treatment for CML, we performed a perspective, sequential analysis using quantitative Southern blot monitoring of BCR gene rearrangements of blood and marrow samples from Cancer and Leukemia Group B (CALGB) study 8761. Patients and Methods: Sixty-four previously untreated adults with chronic-phase CML who were enrolled onto CALGB 8761, a molecular-monitoring companion study to a treatment study for adults with chronic-phase CML (CALGB 9013). Treatment consisted of repetitive cycles of interferon alfa and low-dose subcutaneous cytarabine. Brood and marrow Southern blot quantitation of BCR gene rearrangements was compared with marrow cytogenetic: analysis before the initiation of treatment and at specified points during therapy. Reverse-transcriptase polymerase chain reaction (RT-PCR) analysis was performed to detect residual disease in patients who acheived a complete reponse by Southern blot or cytogenetic analysis. Results: Quantitative molecular monitoring by Southern blot analysis of blood samples was found to be equivalent to marrow monitoring at all time paints. Twelve of 62 (19%) follow-up samples studied by Southern blot analysis had a complete loss of BCR gene rearrangement in matched marrow and blood specimens. Southern blot monitoring of blood sampler was also found to be highly correlated to marrow cytogenetic evaluation at all points, although there were four discordant cases in which Southern blot analysis of blood showed no BCR gene rearrangement, yet demonstrated from 12% to 20% Philadelphia chromosome-positive metaphase cells in the marrow. RT-BCR analysis detected residual disease in five of six patients in whom no malignant cells were detected using Southern blot or cytogenetic analyses. Conclusion: Quantitative Southern blot analysis of blood samples may be substituted for bone marrow to monitor the response to therapy in CML and results in the need for fewer bone marrow examinations, To avoid overestimating the degree of response, marrow cytogenetic analysis should be performed when patients achieve a complete response by Southern blot monitoring. This approach provides a rational, cost-effective strategy to monitor the effect of treatment of individual patients, as well as to analyze large clinical trials in CML. (C) 1997 by American Society of Clinical Oncology.