Shift work which causes circadian disruption is an established cancer risk factor. A large body of experimental and epidemiological data proves that exposure to light at night promotes carcinogenesis in various tissues and accelerates aging . Artificial or natural light through master clock located in suprachiasmatic nuclei of hypothalamus suppresses night peak of melatonin synthesis in the pineal gland. Melatonin is known to exert antioxidant, antigonadotropic, immunostimulating and anticancer effects . Except direct antioxidant action through free radicals scavenging melatonin works as a chronobiotic which tunes cellular clock.