PSMB5 and mantle cell lymphoma: Although the proteasome performs key homeostatic cellular functions, targeted inhibition of the 20S proteasome chymotryptic catalytic subunit PSMB5 is used for the treatment of multiple myeloma (MM) and mantle cell lymphoma (MCL), and three such inhibitors have been licensed (bortezomib, ixazomib and carfilzomib).