A phase I dose-escalation study of MSC1992371A, an oral aurora kinase inhibitor, was carried out in patients with hematologic malignancies. Patients received escalating doses either on days 1-3 and 8-10 (n=36) or on days 1-6 (n=39) of a 21-day cycle. The maximum tolerated doses were 37 and 28 mg/m(2)/day, respectively. Dose-limiting toxicities included severe neutropenia with infection and sepsis, mucositis/stomatitis, and diarrhea. Complete responses occurred in 3 patients. Four disease-specific expansion cohorts then received the dose and schedule dictated by the escalation phase but the study was prematurely discontinued due to hematologic and gastrointestinal toxicity at clinically effective doses.