CHKA and oral cavity squamous cell carcinoma: PER2 proteins are downregulated in oral cancer (Guo et al., 2020), and this decrease in PER2 affects the CDK/CKI cell cycle network and the levels of P53, moreover, it inhibits DNA adduct repair, potentiates the cytotoxicity of oxaliplatin and promotes cell apoptosis in oral squamous-cell carcinoma cells, therefore, periodic oxaliplatin administration in synergy with PER2-mediated PCNA transcription repression promotes chronochemotherapeutic efficacy of OSCC (Tang et al., 2019).