A method of treating a disease characterized by aberrant cell migration and/or invasion includes administering to a subject an effective amount of the peptide of SEQ ID NO:3, an Å6 polypeptide, or an isolated polypeptide consisting essentially of the Link region of human CD44 as indicated in FIG. 17 to modulate a FAK signal transduction pathway for a sufficient period of time to treat the disease. A method of diagnosing a condition characterized by aberrant cell migration and/or invasion includes measuring the effect of these polypeptides on FAK signal transduction activity; wherein a change in FAK signal transduction activity is indicative of said aberrant cell migration or invasion. A method of diagnosing a condition characterized by aberrant cell migration and/or invasion includes imaging FAK signal transduction activity in the presence of these polypeptides.