This is an open-label, dose-escalating trial to evaluate the MTD and/or dose to be used for further development by evaluation of DLT in course 1 and the safety of volasertib when added to standard intensive salvage chemotherapy with DNX-FLA in paediatric patients with AML after failure of first-line therapy. Furthermore, data on efficacy and PK/PD of volasertib in paediatric patients with AML when added to standard intensive salvage chemotherapy will be collected.

Inclusion criteria:

• Patients 3 months to <18 years of age at the time of informed consent
• Patients with AML after failure of the front-line intensive AML therapy
• Lansky score at screening >=50 for patients from 3 months to <12 years
• Karnofsky score at screening >=50 for patients from 12 to <18 years
• Use of highly effective methods of birth-control, if sexually active
• Parents/legal guardians and patients have given written informed consent and informed assent suitable for the respective age group

Exclusion criteria:

• Down syndrome
• Acute promyelocytic leukaemia and treatment-related AML
• QTc prolongation
• LVSF <30%
• Cardiac disease and/or dysfunction
• Active uncontrolled infection
• HIV infection, acute or chronic hepatitis
• Inadequate lab parameters
• Impaired renal function
• Pregnancy or nursing
• Further exclusion criteria apply