The pathologic role of BCR dysregulation in lymphoid malignancies

Signaling of the B-cell receptor (BCR) is crucial for the development of normal B lymphocytes and adaptive immunity. BCR signaling also supports the survival and growth of malignant B-cells in patients with B-cell leukemias or lymphomas (BCL). The mechanism of BCR pathway activation in these diseases includes activating mutations within the BCR complex or downstream signaling components, ligand independent tonic BCR signaling, or BCR stimulation by autoantigens or microbial antigens in the microenvironment of secondary lymphatic tissues. Bruton's tyrosine kinase (BTK) inhibitors and PI3K isoform-selective inhibitors target BCR signaling, and their introduction into the clinic has fundamentally changed the treatment of several B-cell malignancies (chronic lymphocytic leukemia/small lymphocytic lymphoma, mantle cell lymphoma, Waldenstrom's macroglobulinemia, marginal zone lymphoma). This chapter discusses the role of BCR signaling in B-cell malignancies, and how kinase inhibitors blocking BCR signaling interfere with disease biology and benefit patients with B-cell malignancies.