Several recent studies reported that PCSK9 expression was associated with the development and progression of various human cancers, whereas inhibition of PCSK9 expression could attenuate the progression of breast cancer, glioma, hepatocellular cancer, prostate cancer, and lung adenocarcinoma, but promote apoptosis of prostate cancer, glioma, and hepatocellular cancer cells [23]. Here, PCSK9 is linked to breast cancer.