BTK and B-cell chronic lymphocytic leukemia: Novel targeted therapies (e.g., Bruton’s tyrosine kinase (BTK) inhibitor, ibrutinib; phosphoinositide 3-kinase (PI3K) inhibitor, idelalisib; and B-cell lymphoma-2 protein (BCL-2) inhibitor, venetoclax) are rapidly changing the treatment circumstance of CLL [20,21].