BTK and mantle cell lymphoma: Jacobson and colleagues reported that HSP90 inhibition led to the complete loss of BTK and IKKα and downstream loss of phosphorylated ERK1/2 in mantle cell lymphoma cell lines (106).Moreover, HSP90 inhibitor showed to downregulate BTK in cells expressing BTK C481S mutation, which was found to be associated with resistance to BTK inhibitor ibrutinib in MCL and CLL patients (106–108).