PCSK9 and melanoma: In comparisons to tumors produced in C57BL/6 mice, PCSK9 and D374Y allografts generated in Pcsk9−/− mice accumulated less esterified cholesterol (ORO staining) but not active cholesterol (filipin staining) (Fig. 9f), implying a role of tumor-derived PCSK9 in facilitating cholesterol availability to melanoma.