Cancer is perhaps one of the most annoying diseases whose causes are often elusive and unrecognizable. The etiological agents of cancer are difficult to estimate and are not attributed to purely genetic or purely environmental factors. Therefore, cancer research has largely focused on the interaction between genes and environment (Mucci et al., 2001). A large number of studies have investigated the possible causes of various types of cancers, implicating diet, heredity and environment as the main determinants. Most diseases result from complex interactions between a person's genetic makeup and the environmental agents to which they are exposed (NIEHS, 2011). Therefore, the possibility of gene-environment interactions being involved in the occurrence of cancers is being studied worldwide.Gene-environment interactionsA disease occurs when there is an interaction between "genetic susceptibility factors" and “modifiable environmental factors,” as well as variations in the The genetic makeup of an individual influences their susceptibility to environmental factors responsible for disease (CDC, 2000). Therefore, due to genetic variation, some individuals are more susceptible to a particular disease than others, and these variations determine the magnitude of the effect of a particular environmental condition on an individual's disease risk. Can gene-environment interactions be measured “Gene-environment interaction can be defined as that which occurs when “genetic and environmental exposure combine to cause disease in some or all cases” (Brennan , 2002). Because an individual's genetic makeup determines susceptibility to environmental carcinogens, researchers are hard at work amid the document......y Program of the U.S. Department of Health and Human Services. Retrieved September 7, 2011 from http://ntp.niehs.nih.gov/ntp/roc/twelfth/roc12.pdf Travis, RC, Reeves, GK, Green, J., Bull, D., Tipper, SJ, Baker, K., Beral, V. et al. (2010). Gene-environment interactions in 7,610 women with breast cancer: prospective data from the Million Women Study. Lance, 375(9732), 2143-2151. Lancet Publishing Group. Retrieved September 7, 2011 from http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)60636-8/abstract Zhou, W., Liu, G., Miller, DP, Thurston, SW, Xu, LL, Wain, JC, Lynch, TJ et al. (2002). Gene-environment interaction for ERCC2 polymorphisms and cumulative smoking exposure in lung cancer. Cancer Research, 62(5), 1377-1381. Accessed September 7, 2011 from http://cancerres.aacrjournals.org/content/62/5/1377.short