PTK2 and breast cancer: These mice were then examined for the appearance of tumors, in order to gauge the importance of FAK (conditionally deleted in mammary tumor cells of cKO-Wnt1 mice) and its kinase activity (only kinase-defective protein encoded by the KD allele was expressed whereas the floxed allele deleted in mammary tumor cells of cKD-Wnt1 mice) for mammary tumor development and progression.