The study is performed as a randomized double-blinded prospective controlled trial. A total of 72 adult Acetyl salicylic acid (ASA) -exacerbated respiratory disease (AERD) -patients with uncontrolled chronic rhinosinusitis with nasal polyps (CRSwNP) will be recruited. Those negative to ASA-challenge test will not enter the Clinical Trial . All patients entering the Clinical Trial, have undergone earlier ethmoidal surgery (partial/total) and have not gained disease control. F-helicobacter antigen is tested and treatment is given if indicated. The patients are recruited at the Helsinki University Hospital (HUH). The study will be monitored by a professional monitor. Electronic CRF and paper/electronic patient questionnaires provided by HUS will be used (eCRF and patient questionnairea, Granitics).

Randomization and the treatment arms I-II: The patients are randomized to two treatment arms I) ASA- desensitization po tablet daily for 11 months (n=36) II) Placebo po tablet daily for 11 months (n=18).

ASA challenge and desensitization (Primaspan) /Placebo: is conducted according to modified international protocol. FEV1 should be at least 1.5 L and > 60% of predicted before challenge or desensitization. On the first day every patient will receive 25 mg + 25 mg ASA at a hospital setting. On the second day every patient will receive 50 mg + 25 mg ASA at a hospital setting. On the third day every patient will receive 75 mg + 25 mg ASA at a hospital setting. On the fourth day every patient will receive 100 mg + 25 mg ASA at a hospital setting.

During the ASA challenge, patient who is ASA-challenge positive is then randomized and starts the trial so that he/she uses blinded ½ tablet of 250 mg ASA or ½ tablet of placebo daily at home for the next 1 month. After this period of 1 month, the dosing is increased at hospital setting, so that the patient receives blindly 250 mg ASA 1/2 tablet + 1/2 tablet or placebo 1/2 tablet + 1/2 tablet. Thereafter he/she will continue using blindly 250 mg ASA 1 tablet or placebo 1 tablet daily at home for the next 10 months. If the patient does not tolerate the up-dosing of ASA/placebo, he/she will continue using blindly ½ tablet of 250 mg ASA/placebo daily at home for the next 10 months. The total duration of the ASA/placebo treatment is 11 months. We additionally take nasal, blood and urine samples during the trial.

Follow-ups. The symptom questionnaire and interview of side-effects are performed during each visit. Lung function (eNO, nNO, PEF, spirometry) is monitored and the patient will visit doctor and/or nurse at 1, 5, 11, and 12 months post-starting with the treatment. Samples are taken during recruitment visit, before and after ASA-challenge and at 5, 11 and 12 months post-starting with the treatment. We also monitor side-effects, exacerbations, need of medication (po. cortisocteroids; antibiotics) and satisfaction to treatment.

Primary end point is change in nasal endoscopic nasal polyp score at -4 days vs. +11 months post-randomization. Secondary end point is change in Sinonasal Outcome Test -22 (SNOT-22) score at -4 days vs. +11 months post-randomization, and change in relative Forced expiratory volume in 1 second (FEV1 %) without bronchodilator at -1 month vs. +11 months post-randomization.

Safety (complications, adverse effects), costs and loss of productivity between study arms will be compared.

Trial medication will be discontinued, if surgery is needed before the end of follow-up.

Inclusion Criteria: ALL these need to be positive:

• Endoscopic nasal polyp score ≥4
• SNOT-22 ≥30
• Sinus Computed tomography Lund-Mackay score ≥14. The new sinus CT scans are needed if the previous sinus CT scans have been performed over 36 months before recruitment visit or if there is a suspicion of complication of CRS (f.ex. mucocele, invasive fungal rhinosinusitis)
• ≥1 previous partial/total ethmoidectomy surgery.

In addition, patient should have a history of at least one of the following:

>1 oral corticosteroids during the past two years >3 antibiotic courses during the past two years. In patients with contraindication/adverse effects in using oral steroids additional criteria are not required.

Exclusion Criteria:

• complication of CRS (f.e. mucocele, invasive fungal rhinosinusitis)
• bleeding diathesis
• pregnancy/ breastfeeding
• cystic fibrosis
• primary ciliary dyskinesia (PCD)
• sarcoidosis
• granulomatosis with polyangitis (GPA)
• eosinophilic granulomatosis with polyangitis (EGPA)
• immunosuppression (diagnosed Spesific antibody deficiency (SAD), CVI, HIV
• use of biologicals/immunosuppressive medication
• immunotherapy
• Daily use of systemic corticosteroids (Prednisolon 10mg or equivalent) -communication problems (f.e. neurological/psychiatric disease, language skills) -unlikely to comply
• other severe disease
• uncontrolled asthma
• ASA-challenge negative
• gastric ulcer
• anticoagulant treatment
• SSRI-depression medication
• beta-blocker
• severe chronic urticaria
• ASA anaphylaxis

The data is owned by Helsinki University Hospital and University of Helsinki.

The IMP producer (Galena Pharma Ltd., Kuopio, Finland) has packed the IMP according to study protocol and provides a code of each product. The IMP is used double-blinded in their numbered order. The key of the codes are stored in closed envelopes in Hospital´s locked closet. HYKS-institute performs regular study monitoring