PCSK9 and colorectal carcinoma: Amino acid metabolism plays a crucial role in tumor progression and the response to therapy.[14, 15, 28] To determine whether abnormal amino acid metabolism is related to alterations of PCSK9 expression in tumor cells, we cultured primary tumor‐derived and metastasis‐derived human CRC cells (SW480 and SW620 cells) in a medium devoid of individual amino acids.