FOSL1 and breast cancer: Besides c-Fos, FosB, Fra-1 and Fra-2 have also been shown to have a function in progression of various tumour types: FosB is downregulated in poorly differentiated mammary carcinomas (Bamberger et al, 1999), whereas Fra-1 and, partly, Fra-2 overexpression leads to enhanced tumour cell motility and invasion in breast cancer, colorectal cancer and mesothelioma (Milde-Langosch, 2005).