BTK and cancer: PROTACs have been developed targeting proteins important in cancer growth such as BTK (Bruton’s tyrosine kinase), FAK (Focal adhesion kinase), CDK’s (Cyclin-dependent kinases), Bromodomain-containing protein 4 (BRD4), Mcl-1, MDM2 (312–314) for haematological malignancies (315) and solid cancers, including a photo-controlled BRD4 PROTAC for tongue squamous carcinoma (314).