Y-box binding protein 1 (YB-1) is commonly elevated in many human cancers. The cancer-promoting properties of YB-1 are associated with increased resistance to drugs, tumour growth and poor patient outcome. Control of these processes takes place in the nucleus. The precise molecular nature of the active cancer-promoting subtype of YB-1 present in the nucleus, is unknown. Identification of this species will provide the basis for a specific and highly prognostic indicator. This proposal, which builds on our recently published analyses of endogenous YB-1, aims to identify the molecular nature of this cancer-promoting subtype of YB-1 and to determine how it functions. From this knowledge we will develop an antibody that specifically recognises only the nuclear YB-1 species and establish this species as a prognostic indicator for human cancers.