EGF and squamous cell carcinoma: For example, at saturating EGF doses, PI3K inhibition by wortmannin only slightly attenuates ERK phosphorylation in A431 human epidermoid carcinoma and MCF7 human mammary carcinoma cells (over the 2–60 min response period), whereas PI3K inhibition dramatically decreases ERK phosphorylation at low physiological EGF doses13.