Quantification of BCR-ABL transcripts in CML patients in cytogenetic remission after interferon-α-based therapy

We measured using a competitive quantitative polymerase chain reaction-capillary electrophoresis (PCR-CE)-based assay, the levels of bcr-abl transcripts in 44 patients with chronic myeloid leukemia (CML) after interferon-α (IFN-α) therapy, who achieved a major (10 patients, MCR group) or complete (34 patients, CCR group) cytogenetic response. All 34 CCR patients had molecular evidence of residual disease detected in bone marrow samples at the time of best karyotypic response. The median number of bcr-abl transcripts of 34 evaluable patients in the CCR group at the time of complete cytogenetic remission was 4/μg RNA (range 3-4600), while the median number of bcr-abl transcripts of 10 patients in the MCR group at the time of best cytogenetic response was 4490/μg RNA (range 600-23,900) (P = 0.000024). In nine CCR and five MCR patients we were able to quantify the amount of bcr-abl transcript both at diagnosis and after interferon therapy: no statistical difference (P = 0.18) was found between the two groups at diagnosis (median bcr-abl transcripts/μg RNA was 30,000 vs 39,650, respectively). During IFN-α therapy, the two groups were evaluable at the time of major karyotypic conversion: at this point, there was a statistical difference of expression of bcr-abl transcript between the CCR group (17 patients) (median 2700; range 76-40,000) and the MCR group (10 patients) (median 4490; range 600-23,900), respectively (P = 0.046). No differences of bcr-abl amount of transcript were found in patients with CCR obtained either by IFN-α therapy alone (20 patients) vs IFN-α plus ABMT (13 patients) (P = 0.47). We firstly demonstrated that although the CCR and MCR groups were clinically, cytogenetically and molecularly indistinguishable at diagnosis, the two groups could be recognized successfully during interferon therapy based on the level of bcr-abl transcript.