A negative correlation between Fra-1-positivity and ER-positive status has been already observed in breast cancer cell lines and IDC cases.5,7,10,12,34 It could be that, because of the lack of ER, other factors form complexes with Fra-1, and that changes in AP-1 composition, activation or nuclear retention may induce the expression of genes involved in the establishment of an aggressive phenotype.34,35. This evidence concerns the gene FOS and breast cancer.