A half-log increase in BCR-ABL RNA predicts a higher risk of relapse in patients with chronic myeloid leukemia with an imatinib-induced complete cytogenetic response

Purpose: Imatinib induces a complete cytogenetic response (CCR) inmost chronic myeloid leukemia patients in chronic phase. Although CCR is usually durable, a minority of patients relapse. Biomarkers capable of predicting those CCR patients with a higher risk of relapse would improve therapeutic management. Experimental Design: To assess whether changes in BCR-ABL RNA levels are a prognostic biomarker predictive of relapse, we regularly monitored transcript levels [every 3 months (median)] in 90 patients with CCR during 49 months (median) of imatinib therapy. Results: Throughout follow-up, the 20 patients with eventual relapse had higher transcript levels than the durable responders. Major molecular response (MMR; >3-log reduction of BCR-ABL RNA) was attained by 76 patients (12 with subsequent relapse) and was a significant predictor of prolonged relapse-free survival (P = 0.0008). A minimal 0.5-log increase in transcripts (before relapse; experienced by 42 patients, 16 with subsequent relapse) conveyed a significantly shorter relapse-free survival (P = 0.0017). Loss of MMR (transcript increase to <2.5-log reduction, before relapse; experienced by 33 patients, 11 with subsequent relapse) was also predictive of shortened relapse-free survival (P = 0.0003). A complete molecular response (undetectable transcripts by nested PCR) was attained by 28 MMR patients (one with subsequent relapse) and conveyed a significantly prolonged relapse-free survival (P = 0.0052). Conclusions: In chronic myeloid leukemia patients with an imatinib-induced CCR, a minimal half-log increase in BCR-ABL RNA (including loss of MMR) is a significant risk factor for future relapse. The achievement of a complete molecular response imparts longer progression-free survival than the achievement of an MMR.