A fixed dose oral combination (FDC) of decitabine and cedazuridine (Inqovi®), is being developed by Astex Pharmaceuticals (a subsidiary of Otsuka Pharmaceuticals) for the treatment of various cancers like myelodysplastic syndromes (MDS), chronic myelomonocytic leukaemia (CMML), acute myeloid leukaemia (AML), glioma and solid tumours. Decitabine, a DNA methyltransferase inhibitor approved for the treatment of MDS and CMML, is degraded by cytidine deaminase in the gastrointestinal tract and liver, thereby limiting oral bioavailability. Cedazuridine is a proprietary, patented cytidine deaminase inhibitor that, when added to decitabine, increases oral bioavailability of the drug. In July 2020, decitabine/cedazuridine received its first approval in the USA and Canada for the treatment of MDS and CMML. In the USA, it is indicated for use in adults with MDS and CMML, including previously treated and untreated, de novo and secondary MDS with the following French-American-British subtypes (refractory anaemia, refractory anaemia with ringed sideroblasts, refractory anaemia with excess blasts and CMML) and intermediate-1, intermediate-2 and high-risk International Prognostic Scoring System groups. Clinical studies for AML, glioma and solid tumours are underway in several countries worldwide. This article summarizes the milestones in the development of decitabine/cedazuridine leading to this first approval for the treatment of MDS and CMML.