• the disease-free period, defined as the time between the beginning
  
• of the maintenance therapy (AZA or MMF) and the first relapse (minor or major)
  
• or the end of the protocol (at 48 months)
  

• relapse rate
  
• rate of side-effects and intolerance
  
• cumulative doses (AZA, CS, MMF)
  
• AUC for BVAS, SF-36 or VDI
  
• Evolution of titers of ANCA and CRP
  

AASV, including Wegener’s granulomatosis (WG) and microscopic polyangiitis (MPA) and renal limited vasculitis (RLV), are progressive, multisystem, autoimmune diseases which require the prescription of immunosuppressive therapy. Treatment using corticosteroids and cytotoxic drugs has been standardised (ECSYSVASTRIAL project), but relapse rate remains high and treatment-related toxicity is non negligible. The IMPROVE trial aims to reduce this relapse rate by using mycophenolate mofetil (MMF) for maintenance therapy. The potential benefit of MMF has been suggested in a published open and uncontrolled study. Patients with newly diagnosed systemic AASV will be randomly assigned to receive either MMF or reference treatment with azathioprine (AZA), once remission has been obtained with cyclophosphamide and prednisone. MMF and AZA will be continued for a total of 42 months of therapy with concomitant prednisone dose tapering. The study will last 48 months. Hence, within the last 6 months of the study duration, the patients will not receive any immunosuppressive drugs. The primary end-point will the disease-free period, taken as the period of time from remission until relapse or study end; secondary end-points will be adverse events, cumulative damage (assessed using damage score VDI) and immunosuppressive drug cumulative dose.