To explore the involvement of AP-1 in progestin-induced breast cancer growth, we transiently transfected C4HD cells with a p-Flag vector (C4HD-p-Flag) as control, with TAM-67 (C4HD-TAM-67) or A-Fos (C4HD-A-Fos), and also co-transfected them with TAM-67 and A-Fos (C4HD-TAM-67/A-Fos). Here, FOS is linked to breast carcinoma.