Mepolizumab and in Office-office Nasal Polypectomy in Patients With Chronic Rhinosinusitis (CRS).

Inclusion Criteria: 1. Participant 18 years of age or older 2. Patients with a diagnosis of CRS with polyposis according to the criteria of the EPOS2020 guideline: Chronic rhinosinusitis with nasal polyps in adults is defined as presence of two or more symptoms, one of which should be either nasal blockage / obstruction / congestion or nasal discharge (anterior / posterior nasal drip); ± facial pain/pressure; ± reduction or loss of smell; for ≥12 weeks; and either endoscopic signs of nasal polyps, and/or CT changes: mucosal changes within the ostiomeatal complex and/or sinuses. 3. Patients with indication for biologic treatment according to the criteria of the EPOS2020 guideline. Presence of bilateral polyps in a patient who had ESS and three of the following criteria are required: 3.1. Evidence of type 2 inflammation (tissue eos\> 10/hpf\* or blood eos\>250, OR total IgE\> 100). \* Whenever possible histology from previous surgery should be reviewed to confirm if eosinophilic pathology. If the previous surgery was performed more than 2 years earlier, a blood eosinophil count is essential, as the previous biopsy data may not be relevant. 3.2. Need for systemic corticosteroids or contraindication to systemic steroids (≥ 2 courses per yr, OR long term (\>3 months) 3.3. Significantly impaired quality of life (SNOT ≥ 40) 3.4. Significant loss of smell (≥7 VAS) 3.5. Diagnosis of comorbid asthma 4. Basal eosinophil count (BEC) ≥300 cells/µL for surgical naïve patients- or for those who have had surgery and have recurrence . The result of a previous analysis would be valid if it was obtained in a period of time not exceeding one year 5. Patients have been informed and signed consent to participate in the study. Exclusion Criteria: 1. Any serious or uncontrolled systemic or psychiatric illness that prevents a correct cognitive or endoscopic assessment or does not advise participation in the study. 2. Unilateral localized secondary CRS (odontogenic, fungal ball, tumor). 3. Bilateral diffuse secondary CRS (cystic fibrosis; eosinophilic granulomatosis with polyangiitis-S. de Churg-Strauss-; granulomatosis with polyangiitis-S de Wegener-; primary ciliary dyskinesia; selective immunodeficiencies. 4. Pregnancy/ breast feeding. 5. Hypersensitivity to mepolizumab or its excipients. 6. Patients unable to complete the questionnaire or follow prescribed treatment. 7. Patients who are participating in another clinical trial related to polyposis or asthma. 8. Previously documented failure with IL-5/IL-5 receptor biologics