QUANTIFICATION OF RESIDUAL DISEASE IN CHRONIC MYELOGENOUS LEUKEMIA PATIENTS ON INTERFERON-ALPHA THERAPY BY COMPETITIVE POLYMERASE CHAIN-REACTION

Interferon-alpha (IFN-alpha) induces cytogenetic responses of variable degree in patients with chronic myelogenous leukemia (CML). We sought to establish the relationship between BCR-ARL transcript numbers meas ured by competitive 2-step reverse transcription polymerase chain reac tion (RT-PCR) and cytogenetic status in CML patients treated with IFN- alpha. A total of 250 peripheral blood and 55 bone marrow samples from 127 Philadelphia chromosome positive (Ph(+)) and 6 Ph(-)/BCR-ABL(+) C ML patients were investigated. Twenty-one patients were studied at dia gnosis and 112 on treatment. Of the 106 Ph(+) patients treated with IF N-alpha, 24 had a complete cytogenetic response, 21 a partial response , 12 a minor response, 26 no response, and 23 were unknown. Using nest ed RT-PCR, all 305 samples were positive for BCR-ABL transcripts. To s tandardize results for variability in RNA and cDNA quantity and qualit y, we quantified total ABL transcripts in each sample as internal cont rol. The validity of ABL as internal control was shown by comparison w ith glucose-6-phosphate dehydrogenase transcript levels in 145 samples . The median BCR-ABL transcript numbers (and BCR-ABL/ABL ratios expres sed as percentages) were 400/mu g RNA (0.04%) in complete responders, 20,500/mu g RNA (7.1%) in partial responders, 170,000/mu g RNA (21.0%) in minor responders, and 430,000/mu g RNA (58.7%) in nonresponders (P <.001). The cytogenetic results correlated with the BCR-ABL transcrip t numbers (r =.82; P <.001) and BCR-ABL/ABL ratios (r =.84; P <.001). Grouping the ratios BCR-ABL/ABL as less than 2%, 2% to 14%, and greate r than 14% to compare with cytogenetic complete response, partial resp onse, and minor/nonresponse, the concordance between the two methods w as 82% (chi(2) P <.0001). We conclude that quantitative PCR with inter nal controls is a sensitive and reliable method for monitoring patient s on IFN-alpha and reduces the need for repeated marrow investigations . (C) 1996 by The American Society of Hematology.