TXK and hepatocellular carcinoma: BTK is a non-receptor tyrosine kinase belonging to the TEC family, the second largest family of cytoplasmic tyrosine kinases whose other members are TEC (tyrosine kinase expressed in hepatocellular carcinoma), BMX (bone-marrow tyrosine kinase gene on chromosome X), ITK (interleukin-2 (IL-2)-inducible T-cell kinase), and RLK (resting lymphocyte kinase).