JUN and neoplasm: The transcription activator protein, activator protein 1 (AP-1), has been broadly implicated in tumour progression, and many genes involved in cell proliferation, differentiation, malignant transformation and cell invasion are AP-1-dependent.2 Fos-related antigen 1 (Fra-1) is a member of the Fos protein family (c-Fos, Fos B, Fra-1 and Fos-related antigen 2), which are able to dimerize with members of the Jun family, forming AP-1.