A small molecule inhibitor of Bruton's tyrosine kinase (BTK; Bruton agammaglobulinemia tyrosine kinase) with potential antineoplastic activity. Upon administration, orelabrutinib binds to and inhibits the activity of BTK. This prevents both the activation of the B-cell antigen receptor (BCR) signaling pathway and BTK-mediated activation of downstream survival pathways, inhibiting the growth of malignant B-cells that overexpress BTK. BTK, a member of the Src-related BTK/Tec family of cytoplasmic tyrosine kinases, is overexpressed or mutated in B-cell malignancies; it plays an important role in the development, activation, signaling, proliferation and survival of B-lymphocytes.