PTK2 and breast cancer: To further examine the role of FAK in Wnt1-driven mammary tumor growth and metastasis, spontaneously immortalized mammary tumor cells from Ctrl-Wnt1 (i.e., MMTV-Wnt1; Fakfl/fl) mice were prepared, and then transduced with recombinant retroviruses encoding Cre-ERT [31, 36].