If HeLa cells have about 3–4 × 105 receptor molecules on PM which become saturated at EGF concentration of about 4 nM, the human epidermoid carcinoma cell line A431 possesses about 2–3 × 106 EGFR per cell which become saturated at about 25–30 nM of EGF. The gene discussed is EGF; the disease is squamous cell carcinoma.