ACE2 and malignant colon neoplasm: ACE2 was knocked down in gastrointestinal tumor cell lines, including the colon cancer cell line SW480, liver cancer cell line Huh7, gastric cancer cell line HGC, and pancreatic cancer cell line CFPAC1, using RNA interference oligos (RNAi) targeting human ACE2, and the proliferation effects upon serum supplementation were detected by a CCK-8 assay.