This is a Phase I/II clinical study to determine the maximum tolerated dose (MTD), safety, tolerability, pharmacokinetics, and pharmacodynamics of AZD2811 in patients with relapsed AML/high risk myelodysplastic syndrome or treatment-naïve patients not eligible for intensive induction therapy or allogeneic transplantation. The study was also explore the potential clinical activity by assessing anti-tumour activity in patients. The study will be conducted in two parts, designated Part A, dose escalation, and Part B, dose expansion.