Hence, it has been hypothesized that circadian clock genes can regulate or suppress other circadian genes by certain mechanisms, which may also corroborate the finding on simultaneous lower expression levels of circadian gene such as PER1, PER2, PER3, CRY1, CRY2 and BMAL1 in HNSCC (Table 2) [5]. The gene discussed is CLOCK; the disease is head and neck squamous cell carcinoma.