BTK and B-cell chronic lymphocytic leukemia: In the past 5 years, the development of highly active novel agents have made it possible to target key pathogenetic pathways of CLL, including Bruton’s tyrosine kinase (BTK), spleen tyrosine kinase (SYK), and phosphoinositide 3-kinase (PI3K) inhibitors that disrupt the B cell receptor (BCR) signaling pathway, and venetoclax, an antagonist of the antiapoptotic protein BCL-2 (4, 5).