The introduction of small molecule inhibitors, such as Bruton tyrosine kinase (BTK) [7–10], phosphoinositide 3-kinase (PI3K) [11], or B-cell Lymphoma 2 (BCL-2) [12, 13], has changed the treatment paradigm by providing even more effective therapeutic options for CLL patients. The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.