Fluorescence In Situ Hybridization Monitoring of BCR-ABL-Positive Neutrophils in Chronic-Phase Chronic Myeloid Leukemia Patients during the Primary Stage of Imatinib Mesylate Therapy

We describe a method for monitoring chronic myeloid leukemia (CML) patients treated with imatinib that uses fluorescence in situ hybridization (FISH) to detect BCR- ABL in peripheral blood (PB) granulocytes. First, we compared this method, termed Neutrophil- FISH, with interphase FISH (i-FISH) analysis of bone marrow (BM), i-FISH analysis of PB mononuclear cells, and conventional cytogenetic analysis (CCA) of BM in 30 consecutive CML patients. We found the percentage of BCR- ABL-positive neutrophils as determined by Neutrophil-FISH to correlate best with the percentage of Philadelphia chromosome-positive metaphases in the BM determined by CCA (y = 0.8818x + 5.7249; r2 = 0.968). We then performed a serial Neutrophil-FISH study of 10 chronic-phase CML patients treated with imatinib and found that the technique could clearly separate imatinib responders from nonresponders within 12 weeks of drug administration. There was a significant difference in the percentages of BCR- ABL-positive neutrophils between responder (mean ± SD, 18.2% ± 11.8%) and nonresponder (82.4% ± 5.1%) groups at 12 weeks (P <.0001, Student t test). Together with real-time quantitative polymerase chain reaction analysis, Neutrophil-FISH represents another useful method for monitoring CML patients during the primary myelosuppressive stage of imatinib therapy because it is a quick, simple, and reliable method for assessing cytogenetic response.