PCSK9 and cancer: The enzyme proprotein convertase subtilisin/kexin type 9 (PCSK9) is essential in the metabolism of cholesterol, which recent tests in the field of oncology have shown to be a potential biomarker of malignant diseases, while tests in the course of studies suggest that PCSK9 inhibitors, which are used in the treatment of hypercholesterolemia, could also be used in the treatment of some forms of cancer.