HBEGF and thyroid gland carcinoma: By contrast, it has been shown that HB-EGF is a chemotactic factor but not a mitogen for cells expressing HER4 in contrast to its ability to stimulate both chemotaxis and proliferation in cells expressing HER1 (24), suggesting a possible role for HER4 as well as HER1 in mediating HB-EGF-stimulated chemotaxis in thyroid carcinoma cells.