In oral squamous cell carcinoma, KO of PER1 promotes cell growth, proliferation, apoptosis resistance, migration and invasion, accompanied by upregulated mRNA expression of Ki-67, mouse double minute 2 homolog (MDM2), B-cell lymphoma 2 (BCL-2), MMP2, MMP9, and downregulated expression of cellular MYC proto-oncogene (C-MYC), p53, BCL-2 associated X protein (BAX), tissue inhibitor of metalloproteinases 2 (TIMP-2) (116). Here, PER1 is linked to oral cavity squamous cell carcinoma.