The Janus kinases (JAK1, JAK2, JAK3 and TYK2) are a family of intracellular tyrosine kinases that regulates cell proliferation, differentiation, survival, and embryological processes.74 Oncogenic mutations can result in activation of the JAK–STAT pathway, contributing to the progression of several cancers, including haematological malignancies and some solid tumours.75 The JAK active site contains a conserved cysteine residue, like that of BTK and EGFR, and therefore covalent inhibition of this kinase is possible. The gene discussed is BTK; the disease is cancer.