MUC5AC and nasal cavity polyp: Also, transforming growth factor-α is highly expressed in nasal mucosa of chronic rhinosinusitis with nasal polyps and is deeply involved in MUC5AC gene induction and in mucus hypersecretion.23 During endoscopic polypectomy, the epithelium, eosinophils, fibroblasts, vascular endothelium and macrophages, as rich sources of epidermal growth factor and transforming growth factor-α, are removed, which leads to a decrease in the concentration of these mediators in nasal secretions after removal of the nasal packing.