BACKGROUND: In patients with acute coronary syndrome (ACS), alirocumab reduced the risk of recurring ischemic events. ODYSSEY J-IVUS assessed the effect of alirocumab on coronary atheroma volume in Japanese patients recently hospitalized with ACS and hypercholesterolemia, using intravascular ultrasound imaging analysis.Methods and Results:Patients (n=206) who at index ACS diagnosis either had low-density lipoprotein cholesterol (LDL-C) ≥2.59 mmol/L (≥100 mg/dL) despite stable statin therapy, or were not on statins with LDL-C levels above target after statin initiation, were randomized (1:1) to alirocumab (75 mg every 2 weeks [Q2 W]/up to 150 mg Q2 W), or standard of care (SoC; atorvastatin ≥10 mg/day or rosuvastatin ≥5 mg/day) for 36 weeks. The primary efficacy endpoint (week [W] 36 mean [standard error] percent change in normalized total atheroma volume [TAV] from baseline) was -3.1 (1.0)% with SoC vs. -4.8 (1.0)% with alirocumab (between-group difference: -1.6 [1.4]; P=0.23). W36 absolute change from baseline in percent atheroma volume was -1.3 (0.4)% (SoC) and -1.4 (0.4)% (alirocumab; nominal P=0.79). At W36, LDL-C was reduced from baseline by 13.4% (SoC) vs. 63.9% (alirocumab; nominal P<0.0001). In total, 61.8% (SoC) and 75.7% (alirocumab) of patients reported treatment-emergency adverse events. CONCLUSIONS: In Japanese patients with ACS and hypercholesterolemia inadequately controlled despite statin therapy, from baseline to W36, a numerically greater percent reduction in normalized TAV was observed with alirocumab vs. SoC, which did not reach statistical significance.