MUC5AC and nasal cavity polyp: Indeed, the present study provided evidence that EGF at 10–100 ng/ml, which concentration is close to the values in vivo and reported by others [5, 15–18], directly leads to upregulation of MUC5AC expression in HNECs; thus confirming the role of EGF system in regulating goblet cell mucin expression in nasal polyps.