Temperatures cause a variety of physiological changes, e.g. of blood composition, blood pressure ⁹ and circadian rhythms ¹⁰, which in turn are believed to contribute to an increased mortality/incidence of breast cancer ^11,12,13,14. Published laboratory studies have reported that melatonin might have cancer-preventive activities ^11,12,13,14. Melatonin has been observed to exert potent inhibition on cancer growth by acting as natural anti-angiogenic molecule, with a following opposition or angiogenesis-dependent cancer proliferation ¹⁵. This has been demonstrated in certain human breast cancer cell lines such as MCF-7, with additional in-vivo effects on breast oncogenesis in various rat models ¹⁵. Melatonin (N-acetyl-5-methoxytryptamine) is a hormone secreted by the pineal gland of vertebrates, which controls several physiological functions associated with circadian rhythm ^10,16. Temperature is a major regulator of circadian rhythms ¹⁶. Circadian rhythms control many physiological activities. Synchronization of biological clocks to environmental time is adaptive and important for physiological homeostasis and for the proper timing of species-specific behaviors ¹⁷. A number of investigations have been conducted to examine the effects of temperature and light on melatonin rhythms ¹⁸, see Table V. Based on our analysis, we proposed a second order equation (y = a + bx + cx² ) to describe the correlation between the average temperature and mortality rates. This model was best described the relationship between the two parameters. Based on this model, the estimated temperature (T_e) values at which the mortality rates are low is in the range 49< T_e < 11° C.