In a series of experiments using immunocompetent syngeneic mice and four cancer cell lines (B16F10—melanoma, 4T1—mammary carcinoma, MC38—colon adenocarcinoma, and CT26—undifferentiated colon carcinoma), the authors started by showing that tumors resulting from inoculation of PCSK9 knock out cells, obtained through CRISPR-cas9 gene editing, displayed significant growth retardation compared to wild-type counterparts. Here, PCSK9 is linked to cancer.