PCSK9 and atherosclerosis: For example, when we target LDL-cholesterol to prevent atherosclerosis in a patient by prescribing a PCSK9 inhibitor, we may not only aim to reduce LDL-cholesterol but also to reduce plasma (free) PCSK9 concentration [7] and use this marker to monitor target engagement and understand whether increasing the dose of the PCSK9 inhibitor in case of insufficient LDL-cholesterol reduction is rational (see also step 6).