Platzbecker U, et al. - Authors determined whether or not measurable residual disease (MRD)-guided pre-emptive treatment with azacitidine could prevent relapse in patients with advanced myelodysplastic syndromes (MDS) or acute myeloid leukaemia (AML). Haematological relapse in MRD-positive patients with MDS or AML who are at high risk of relapse can be prevented or substantially delayed with pre-emptive therapy with azacitidine. For patient outcomes, continuous MRD negativity during regular MRD monitoring might be prognostic. Neutropenia, occurring in 85% of patients was the most common (grade 3–4) adverse event.