The difference in primary tumor growth between FAK-depleted cells (Figure 6a) and systemic FAK inhibition by PF-562271 (Figure 6d) suggests that FAK plays an important role in governing the composition or activity or both of nontumor cells in the tumor microenvironment, including the potential recruitment of systemic cell populations required for optimal mammary tumor growth and progression. This evidence concerns the gene PTK2 and breast cancer.