Both FGF and WNT pathways play important roles in embryonic development, stem cell self-renewal and are frequently deregulated in breast cancer. To study the cooperation between FGF and WNT signaling, we have generated a mouse model, MMTV-WNT1/MMTV-iFGFR1 (WNT/iR1), in which we could chemically overactivate iFGFR1 in a ligand-independent manner.