Complete clearance of Ph+ metaphases after 3 months is a very early indicator of good response to imatinib as front-line treatment in chronic myelogenous leukemia.

Aim: To address the incidence and the prognostic role of a very early standard complete cytogenetic response (CCyR) or all Ph– metaphases (MET–, when <20 cells were evaluable). Methods: We revised 182 chronic phase chronic myelogenous leukemia patients treated with frontline imatinib (IM) at two institutions from June 2002 to June 2011. Results: After 3 months of treatment, 138 patients (75.8%) achieved CCyR/MET– while 44 patients (24.2%) still presented Ph+ metaphases (MET+) (<33%, 24 patients; ≥33%, 20 patients). On univariate analysis, palpable spleen enlargement (p < 0.001), WBC count >100.0 × 109/l at onset (p < 0.001), and male gender (p = 0.019) had a negative impact on achievement of CCyR/MET– at 3 months. Among patients with CCyR/MET– after 3 months, there were 15 failures (10.8%) compared to 21 (47.7%) among patients with MET+ (p < 0.001). The 5-year overall survival was 97.0% in patients CCyR/MET– at 3 months and 91.8% in patients MET+ at 3 months (p = 0.277); the 5-year progression-free survival was 88.2% in patients CCyR/MET– at 3 months and 48.4% in patients MET+ at 3 months (p < 0.001). Conclusions: The achievement of CCyR/MET– at 3 months seems to have prognostic relevance and could be a very early and useful indicator of an excellent response to IM beyond European LeukemiaNet guidelines.