IFNB1 and myeloid sarcoma: Thus, we have performed a post-hoc analysis of data from a large international, non-interventional, prospective cohort study (NCT00787657; BEACON: BEtaferon prospective study on Adherence, COping and Nurse support), including patients with MS starting treatment with interferon beta (IFNB)-1b within 6 months before study entry.