Profiling the long-term risk of severe adverse events in a cohort of multiple sclerosis patients treated with different treatment sequences: Results from the Italian Multiple Sclerosis and Related Disorders Registry (I-MS&RD) (ProSA study)

Background: In multiple sclerosis (MS), real-world evidence supports early intensive treatment (EIT) with high-efficacy therapies (HET) over escalation (ESC), although comparative data on long-term safety across sequences remain limited. Objective: To compare the incidence of infections and neoplasms in patients treated with different treatment sequences. Methods: Data were extracted from the Italian MS and Related Disorders Register. DMTs were classified as moderate-efficacy treatment (MET), continuous HET (C-HET) or pulsed HET (P-HET). Six therapeutic sequences were reconstructed: MET-only, C-HET-only, P-HET-only, MET→C-HET, MET→P-HET and P-HET→MET. Incidence rates (IRs; per 1000 person-years) and incidence rate ratios (IRRs) were estimated using multivariable Poisson regression, adjusting for age, sex, Expanded Disability Status Scale (EDSS), disease duration, MS phenotype and prior relapse activity. Results: A total of 37,375 patients were included in the analysis, with a median duration of treatment exposure of 8.8 years. Infection risk was significantly higher with C-HET-only (IR, 24.82; IRR, 3.12), P-HET-only (IR, 13.43; IRR, 1.69), MET→C-HET (IR, 10.46; IRR, 1.32) and MET→P-HET (IR, 12.30; IRR, 1.55) versus MET-only (IR, 7.94), while P-HET→MET showed no significant difference from MET-only (IR, 7.67; IRR, 0.97). Regarding neoplasm incidence, P-HET-only showed the lowest rates (IR, 0.18; IRR, 0.24), whereas it was significantly higher in C-HET-only (IR, 1.33; IRR, 1.79) and MET→C-HET (IR, 1.01; IRR, 1.36) versus MET-only (IR, 0.74). Conclusions: This is the first real-world study to compare the safety of different sequences in a national registry. ESC strategies did not confer a long-term safety advantage over EIT. Among HET regimens, C-HET was associated with the greatest risk of both serious infections and neoplasms, whereas P-HET showed the lowest neoplasm incidence.