No advantage of Imatinib in combination with hydroxyurea over Imatinib monotherapy: a study of the East German Study Group (OSHO) and the German CML study group.

INTRODUCTION The combination of Imatinib (IM) and hydroxyurea (HU) was explored for the treatment of chronic myelogenous leukemia (CML). METHOD After in vitro testing and a phase I study (n = 20), 59 patients were randomized in the IM/HU and 29 in the IM arm. According to protocol, 49 propensity-score matched IM patients were included from the CML-IV study. RESULTS Additive specific inhibition of CML cells by IM/HU was detected in vitro. HU 500 mg qd in combination with IM 400 mg qd proved feasible in the phase I study. Overall, no significant difference with respect to major molecular response (MMR) at 18 months (IM/HU and IM 66%; primary endpoint) was observed. Significant differences were noted for MMR at 6 months (p = 0.04) and for cumulative incidences of adverse events (p = 0.03) in favor of IM monotherapy (secondary endpoints). CONCLUSION IM/HU combination was more potent in selectively inhibiting CML cells in vitro, but not superior to IM in vivo. (NCT02480608).