BCR/ABL level at 6 months identifies good risk CML subgroup after failing early molecular response at 3 months following imatinib therapy for CML in chronic phase

It is unclear if patients with CML treated with imatinib who fail to achieve BCR/ABL transcript levels <10%(IS) at 3 months i.e. an early molecular response (EMR) have a better prognosis if they achieve a response by 6 months. We reviewed 320 patients with chronic myeloid leukemia (CML) in chronic phase receiving Imatinib therapy with 3 and 6 month BCR/ABL transcript levels available, and divided them into four groups. Group I (achieved an EMR at 3 months), Group II (did not achieve an EMR at 3 months, but achieved a transcript level of <1% at 6 months), Group III (did not achieve an EMR at 3 months, then at 6 months achieved a level between 1% and 10%) and Group IV (failed to achieve a response at 3 and 6 months). Compared to Group I, Group IV showed significantly worse freedom from treatment failure (FTF; 93.1% vs 69.0%, P < 0.001), progression free survival (97.7% vs 77.3%, P < 0.001) and overall survival (98.3% vs 78.9%, P < 0.001). While, group III showed inferior PFS (98.3% vs 90.4%, P = 0.013) and OS (97.7% vs 90.4%, P = 0.037), but no difference in FTF (93.1% vs 92.0%, P = 0.520). There were no significant differences between Groups I and II. A BCR/ABL transcript level at 6 months can identify a "good-risk" subgroup among patients who fail to achieve an EMR on Imatinib therapy for CML.