Purpose: Interferon alfa (IFN-alpha) induces complete cytogenetic remission in a significant minority of patients with chronic myelogenous leukemia (CML). To date, use of the polymerase chain reaction (PCR) has suggested that residual disease is present in virtually all these individuals at median follow-up intervals of approximately 1 year after initial achievement of cytogenetic remission. We sought to determine the PCR status of CML patients with very long continuous complete cytogenetic remissions on IFN-alpha.
Patients and methods: Blood and/or bone marrow samples from 18 CML patients maintained in continuous cytogenetic remission by IFN-alpha for at least 1 year were studied for residual BCR-ABL mRNA by single-step reverse-transcriptase (RT)-PCR methodology, followed by detection of the amplification product by the hybridization protection assay (HPA).
Results: Ten of 18 patients showed RT-PCR negativity for BCR-ABL. The median duration of continuous complete cytogenetic remission at the time of sample collection for the negative patients was 42 months versus 21 months for the patients whose tests remained positive (P = .05).
Conclusion: Very long-term follow-up of IFN-alpha-treated CML patients in continuous complete cytogenetic remission is associated with a decrease in the number of BCR-ABL transcripts to a level below that detectable by the RT-PCR assay used in this study.