Notably, it contains amino acids of functional relevance, such as cysteine 481 (Cys 481), which lies within the ATP-binding pocket and is crucial for its activity. Also, Cys 481 is the covalent binding target of the BTK inhibitor ibrutinib, an irreversible inhibitor used in the treatment of B-cell neoplasms. This evidence concerns the gene BTK and B-cell neoplasm.