Abstract Details Title Serum NfL in MS Patients Treated with Cladribine: Course and Predictive Value Topic Multiple Sclerosis Presentation(s) P1 - Poster Session 1 (8:00 AM-9:00 AM) Poster/Presentation Number 3-006 Objective We here aimed to assess the impact of CLAD on serum neurofilament light chain (sNfL), a biomarker for neuroaxonal damage. Moreover, we investigated whether sNfL at baseline and at 12 months from CLAD start can predict treatment response. Background Cladribine (CLAD) acts as semi-selective immune reconstitution therapy (IRT) for patients with multiple sclerosis (MS). As such, short treatment cycles in year one and two promise long-term disease control. Design/Methods We included 14 patients with MS about to start CLAD and assessed sNfL values at baseline (BL) and at the end of the first treatment year (12 months from BL). Long-term clinical and radiological data were extracted from medical records. Disease activity was classified according to relapses, MRI activity and EDSS progression. We also calculated a time to loss of "no evidence of disease activity (NEDA)" analysis to evaluate the predictive value of sNfL. Results Patients (12/14 female, mean age 35 ± 9 years, median EDSS 1.75 range 0 - 3.5) were followed-up for 39 (± 9) months after CLAD start. A breakthrough disease was recorded in 36% (5/14) while 64% had no or mild disease activity. The sNfL was significantly reduced by CLAD therapy (mean: 24,72 pg/ml to 8,75 pg/ml, p = 0.0008) and increased in only one patient (from 4,63 pg/ml to 5,55 pg/ml). SNfL values at BL and 12 months did not correlate with long-term disease control. Conclusions CLAD therapy prevents neuroaxonal damage as reflected by sNfL. Most patients had no or only mild disease progression on long-term outcome. SNfL at the end of the first treatment cycle appears no suitable marker to predict long-term treatment response. Authors/Disclosures Tobias Moser PRESENTER Mr. Moser has nothing to disclose. No disclosure on file