An inhibitor of the Bromodomain and Extra-Terminal (BET) family of proteins, with potential antineoplastic activity. Upon administration, mivebresib binds to the acetyl-lysine binding site of BRD-containing protein(s), thereby preventing the interaction between those proteins and acetylated histones. This disrupts chromatin remodeling, prevents the expression of certain growth-promoting genes, and leads to an inhibition of cell growth in susceptible tumors.