With sequence homology to erbB-1, -2, -3 -4 or HER-1, -2, -3 -4, EGFR is a type I receptor tyrosine kinase. It attachesitself to amphiregulin, betacellulin, heparin-binding EGF(HB-EGF), transforming growth factor (TGFa), andepiregulin. Tumours of the breast, brain, bladder, lung,stomach, head and neck, oesophagus, cervix, vulva, ovary,and endometrial all overexpress EGFR. Squamous cellcarcinomas are where it is most frequently found.