Background: CLASSIC-MS (NCT03961204) explores the long-term efficacy and durability of effect of cladribine tablets (CladT; cumulative dose 3.5 mg/kg over 2 years) beyond the 2 annual treatment courses in patients with relapsing multiple sclerosis (MS) enrolled in CLARITY, with/without CLARITY Extension trials, with the aim of informing future treatment choices. Objectives: Interim analysis of long-term outcomes for patients with MS originally enrolled in the parent trials, as part of the CLASSIC-MS study. Methods: CLASSIC-MS is an exploratory, low-interventional, ambispective Phase IV study of patients previously enrolled into Phase III parent trials who had received ?1 course of CladT or placebo. We report an interim analysis of long-term responder rates for a small population of patients with relapsing MS who were previously enrolled in CLARITY with/without CLARITY Extension. Long-term responder status was defined as: A) not requiring further disease-modifying therapy (DMT) treatment until ?4 years after last parent study dose (LPSD), or B) no evidence of disease reactivation based on clinical outcomes in the 4 years following LPSD. Analyses are descriptive. Results: The interim population comprised 93 patients (61% female; mean EDSS score, 4.06±2.00 at CLASSIC-MS baseline), with a median time since LPSD of 10.4 (range 9.5?14.2) years; 93.5% were exposed to CladT in the parent trials. Overall, 82.8% were long-term responders by definition A, and 36.6% by definition B. In addition, 68.8% of patients enrolled to CLASSIC-MS received no subsequent DMT treatment after LPSD. 45% of participating patients were actively employed at the time of CLASSIC-MS enrollment. Conclusions: We report an interim analysis of a small population of patients with relapsing MS from CLARITY with/without CLARITY Extension who are participating in CLASSIC-MS. Findings show that while 3 out of 5 participating patients had disease reactivation during 4 years since LPSD, only 1 in 5 required further DMT treatment during these 4 years. Results from the full analysis set of the CLASSIC-MS study will be shown in the final presentation.