Per1 can also regulate downstream tumor-related genes Ki-67, p53, c-Myc, Bax, MDM2, MMP9, and Bcl-2 in HNSCC (head and neck squamous cell carcinoma) (Li et al., 2016b, Gery et al., 2006). The gene discussed is MMP9; the disease is head and neck squamous cell carcinoma.