Therapy with Bruton’s tyrosine kinase (BTK) inhibitors such as ibrutinib (IBR) and ACP-196 (acalabrutinib) for lymphomas, including mantle cell lymphoma (MCL), is a prime example of such a targeted therapeutic approach, although drug resistance occurs in a large subset of patients, either as a primary event or over time [2–4]. The gene discussed is BTK; the disease is mantle cell lymphoma.