Background: Homozygous familial hypercholesterolemia (HoFH) is a rare genetic lipid disorder characterized by markedly elevated LDL-C and premature ASCVD. For HoFH patients (pts) with complete loss of low-density lipoprotein receptor (LDLR) function in both copies of the LDLR gene (null mutations) and some other HoFH pts, statins and PCSK9 inhibitors have limited to no efficacy, presenting a great unmet medical need. The efficacy and safety of evinacumab (EVIN; an angiopoietin-like protein 3 inhibitor) in HoFH pts was assessed during the double-blind treatment period (DBTP) of a phase 3 trial (NCT03399786). Objective: To examine longer-term efficacy and safety of EVIN in pts with HoFH who participated in the subsequent open-label treatment period (OLTP) of this phase 3 study. Methods: Patients with HoFH on stable lipid-lowering therapies (± lipoprotein apheresis) and screening LDL-C ≥70 mg/dL who completed the 24-week DBTP entered the 24-week OLTP and received IV EVIN 15 mg/kg every 4 weeks. Results: In total, 64 pts completed the DBTP and received open-label EVIN. Mean (standard deviation [SD]) baseline LDL-C at DBTP entry was 250.5 (162.3) mg/dL. From baseline to Week 48, EVIN reduced mean LDL-C by 46.3% (mean [SD] reduction of 134.3 [117.3] mg/dL). At Week 48, mean LDL-C reductions with open-label EVIN were 42.7% and 55.8% for pts who received EVIN (n=44) vs placebo (n=20) during the DBTP, respectively ( Figure ). LDL-C reduction observed at Week 48 was similar for pts with null/null mutations (n=19; 47.2%) versus non-null/null mutations (n=39; 45.9%). Adverse events (AEs) occurred in 47 pts (73.4%) during the OLTP; the most common were nasopharyngitis (9.4%) and headache (9.4%). During the OLTP, serious AEs occurred in 7 pts (10.9%; all pts received EVIN during the DBTP); none were considered related to study treatment. Conclusions: In pts with HoFH, EVIN showed substantial and sustained LDL-C reduction regardless of LDLR function and was generally well tolerated.