Bruton's tyrosine kinase (Btk) is a cytoplasmic protein tyrosine kinase belonging to the tyrosine kinase expressed in hepatocellular carcinoma (Tec) family of non‐receptor tyrosine kinases (TFKs),1 which also include Tec, interleukin (IL)‐2‐inducible T cell kinase (Itk), resting lymphocyte kinase (Rlk) (also called T cell‐expressed kinase), and bone marrow‐expressed kinase (Bmx). The gene discussed is BTK; the disease is hepatocellular carcinoma.