The effectiveness of immunotherapy for most cancer patients remains low, with approximately 10-30% of those treated surviving. Thus, much effort is being put into finding new ways to improve immune checkpoint therapy. Our review concludes that inhibition of proprotein convertase subtilisin/Kexin type 9 (PCSK9), which plays a critical role in regulating cholesterol metabolism, can cause movement of T cells toward tumors, with increased sensitivity to immune checkpoint therapies. We searched PubMed, NCBI, Scopus, and Google Scholar for the published articles without limitations on publication dates. We used the following terms: "PCSK9", "Cancer", "Immune Checkpoint", and "Cancer Prognosis" in the title and/or abstract. Our search initially revealed 600 records on the subject and stored them in the used databases under EndNote X8 management software. A total of 161 articles were selected and through a careful review, 76 were included in our research. We concluded that PCSK9 reduces the number of LDL receptors (LDL-R) on the cell surface, which is linked to its ability to regulate cholesterol levels in the body. Also, we discuss how suppressing PCSK9 leads to the MHC-1 accumulation on the surface of cancer cells, which results in T lymphocyte invasion. Finally, we believe that inhibiting PCSK9 may be an effective strategy for improving cancer immunotherapy.