FOSL1 and breast cancer: We isolated cells from primary mammary tumors and generated tumor cell lines, and consistently found that the expression of Gata3 and E-Cad was abrogated and the expression of Twist and Fosl1 (encoding Fra1) was enhanced in p18-/-;Brca1MGKO (Brca1 deficient) cells relative to the expression in p18-/- (Brca1 proficient) counterparts (Figure 1B, Figure S1A).