Ibrutinib and osimertinib are representative examples of covalent inactivators of Bruton tyrosine kinase (BTK) for the treatment of mantle cell lymphoma and chronic lymphocytic leukemia and epidermal growth factor receptor (EGFR) for the treatment of non-small-cell lung cancer, respectively [27,28]. The gene discussed is EGFR; the disease is B-cell chronic lymphocytic leukemia.