EGFR and cancer: This is due to the fact that: (1) CD44v6 is a marker for colon CSCs (180, 385); (2) CD44v6 can act as co-receptor for at least three RTKs (c-Met, VEGFR-2, and EGFR) (103, 236, 401), and many of the oncogenic functions of CD44v6 can be attributed to downstream signaling induced by these RTKs; and (3) CD44v6 is highly expressed in many cancers.