Bruton Tyrosine Kinase (BTK) is an enzyme that plays a crucial role in the signaling pathways of immune cells, particularly B cells. It is essential for the development and activation of these cells, which are vital for the body's immune response. Mutations in the BTK gene can lead to immunodeficiencies, such as X-linked agammaglobulinemia, where individuals have a reduced ability to produce antibodies. BTK is also a target for certain cancer therapies, especially in treating B-cell malignancies like chronic lymphocytic leukemia (CLL). Inhibitors of BTK can block its activity, helping to slow down the growth of cancer cells and improve patient outcomes.