Melatonin is a neuroendocrine hormone secreted by the pineal gland to transduce the body's circadian rhythms. An internal 24 hour time keeping system (biological clock) regulated by melatonin, controls the sleep-wake cycle. Melatonin production is a highly conserved evolutionary phenomenon. The indole hormone is synthesized in the pinealocytes derived from photoreceptors. Altered patterns and/or levels of melatonin secretion have been reported to coincide with sleep disorders, jetlag, depression, stress, reproductive activities, some forms of cancer and immunological disorders. Lately, the physiological and pathological role of melatonin has become a priority area of investigation, particularly in breast cancer, melanoma, colon cancer, lung cancer and leukemia. According to the 'melatonin hypothesis' of cancer, the exposure to light at night (LAN) and anthropogenic electric and magnetic fields (EMFs) is related to the increased incidence of breast cancer and childhood leukaemia via melatonin disruption. Melatonin's hypothermic, antioxidant and free radical scavenging properties, attribute it to an immunomodulator and an oncostatic agent as well. Many clinical studies have envisaged the potential therapeutic role of melatonin in various pathophysiological disorders, particularly cancer. A substantial reduction in risk of death and low adverse effects were reported from various randomized controlled trials of melatonin treatment in cancer patients. This review summarizes the physiological significance of melatonin and its potential role in cancer therapy. Furthermore, the article focuses on melatonin hypothesis to represent the cause-effect relationship of the three aspects: EMF, LAN and cancer.

: Carcinoma breast is the most common cancer among women worldwide and is the malignant neoplasm affecting and causing mortality among women.. The main objectives of the present study were to assess the knowledge regarding risk factors and its preventive measures of carcinoma breast among urban and rural Indian women. A descriptive research design was used to assess the knowledge regarding risk factors and its preventive measures of carcinoma breast among women in selected urban and rural areas of Tirupati, India. A total of 100 women were selected from urban and Rural areas by convenient sampling technique. The tool used for conducting the study was structured questionnaire on knowledge risk factors and its preventive measures of carcinoma breast. The knowledge on risk factors, out of 50 urban women i.e., 30 (60%) had moderate knowledge, 19 (38%) had inadequate knowledge and only 1 (2%) had adequate level of knowledge regarding risk factors of carcinoma breast adequate knowledge with the mean and standard deviation 15.6 and 3.423. Whereas in rural women, out of 50, majority i.e., 28 (56%) had inadequate knowledge followed by 19 (38%) had moderate knowledge and only 3 (6%) had adequate knowledge with the mean and standard deviation 14.58 and 4.978. It is concluded that there was difference between urban and rural women knowledge on risk factors and its preventive measures of carcinoma breast. The findings suggest that extensive health education programs need to be planned to bring awareness among urban and rural women.