Aims: Evaluate efficacy and safety of alemtuzumab over 6 y in patients who initiated alemtuzumab after receiving SC IFNB-1a in CARE-MS I.

Methods: At investigator discretion, patients in TOPAZ can receive additional as-needed alemtuzumab (≥12 months apart; no criteria), or receive another DMT (at any time). MRI disease activity was defined as new gadolinium (Gd)-enhancing or new/enlarging T2 hyperintense lesions.

Results: Of 139 patients initiating alemtuzumab in the extension, 117 (84%) completed Y2 of TOPAZ (Y6 after initiating alemtuzumab); 67% received neither additional courses of alemtuzumab nor another DMT. At Y6, the annualised relapse rate was 0.19, and 70% of patients had stable/improved EDSS scores from CARE-MS I baseline. After initiating alemtuzumab, 69% were free from 6-month confirmed disability worsening and 28% had 6-month confirmed disability improvement. At Y6, 62% were free of MRI disease activity, 82% were free of new Gd-enhancing lesions, and 62% were free of new/enlarging T2 hyperintense lesions. Median percent cumulative brain volume loss (BVL) from CARE-MS I baseline was -1.99% over 8 total study y; -1.49% occurred over Y0-2 with SC IFNB-1a, and -0.23% occurred over 6 y with alemtuzumab. Safety was consistent with the alemtuzumab arm of the core and extension studies.

Conclusions: Alemtuzumab improved clinical, MRI, and BVL outcomes in patients who initiated alemtuzumab after receiving SC IFNB-1a in CARE-MS I. These improved outcomes were maintained over 6 y in the absence of continuous treatment, with a consistent safety profile that is manageable and acceptable.