302. Efficacy of Mycophenolate mofetil for remission maintenance in ANCA associated vasculitis depends on ANCA specificity

Background/ Objectives: Mycophenolate mofetil is an anti-metabolite used for prevention of transplant rejection and treatment of autoimmune disease. Its clinical utility in ANCA associated vasculitis has been assessed for both relapse prevention and induction, as an alternative to cyclophosphamide. The IMPROVE trial2 aimed to demonstrate that mycophenolate mofetil was superior to azathioprine for the prevention of relapse of ANCA associated vasculitis after cyclophosphamide and steroid induction. The results demonstrated a higher relapse rate in patients treated with mycophenolate mofetil compared to azathioprine but it the association of efficacy with ANCA subtype was not explored. Methods: Eligibility for IMPROVE required a new diagnosis of GPA or MPA with a positive MPO or PR3-ANCA and age ≥ 18 years. A post-hoc analysis of the IMPROVE database was performed to assess differences in relapse free survival between mycophenolate and azathioprine treatment groups according to MPO or PR3-ANCA specificity using the Kaplan-Meier method. Results: Of 159 patients randomised in the trial 55 (35%) were MPO-ANCA and 103 (65%) PR3-ANCA positive (1 patient was ANCA negative). Patients were randomised to either Mycophenolate mofetil (MPO-ANCA 32, PR3-ANCA 51) or azathioprine (MPO-ANCA 26, PR3-ANCA 57). Patients of either ANCA specificity were well matched in ter of age and entry creatinine. There was no difference in mean relapse free survival in patients with MPO-ANCA 174.4 days for either treatment group (p=0.97). In patients with PR3-ANCA the mean relapse free survival was 165.6 days for the azathioprine versus 126.8 for the mycophenolate mofetil treatment groups (p=0.01). Conclusions: This post-hoc analysis found no difference in time to relapse between mycophenolate mofetil and azathioprine for the MPO-ANCA subgroup, but a reduction in time to relapse with mycophenolate mofetil compared to azathioprine for the PR3-ANCA subgroup. These results are consistent with those observed for remission induction in the MYCYC1 trial and suggest that azathioprine is a preferred relapse prevention treatment for PR3-ANCA vasculitis after cyclophosphamide induction. Disclosures: Non