PF-9363 (CTx-648) is a first-in-class, oral inhibitor of the KAT6A/B histone lysine acetyltransferases (HATs) for the treatment of ER+/luminal & KAT6A+ breast cancer discovered by Melbourne’s Cancer Therapeutics CRC (CTxT) and Pfizer, San Diego. This article discusses why the molecule is scientifically notable in drug discovery for epigenetic targets and transferable scientific insights from its decade-long KAT6 campaign including its target rationale, hit-finding and lead optimization, synthesis and relevant clinical data.