C/EBPβ is a differentiation factor for the mammary epithelium and is produced, through alternative initiation of translation, in three isoforms: the transcriptional activators liver activating protein 1 and 2 (LAP1 and LAP2), and the LIP, which can inhibit C/EBPβ-mediated gene activation.20, 21, 22 C/EBPβ has been reported to be deregulated in breast cancer but its role in cancer progression is not fully elucidated (reviewed in Zahnow22). This evidence concerns the gene CEBPB and breast carcinoma.