A comparison of trends in the incidence rates for major cancers during the past decade showed that in Korea, the age-adjusted incidence rates of colorectal cancer between 1999 and 2010 markedly increased from 27 to 49.8 per 100,000 (annual change, 6.3%) in men and from 17.1 to 26.4 per 100,000 in women (annual change, 4.7%) while those of stomach, liver, lung, and cervical cancer decreased (Fig. 4). When compared with other Asian countries [3], the age-adjusted colorectal cancer incidence in men ranked the highest in Korea, followed by Israel, Japan, and Singapore, and that in women ranked 4th highest among Asian countries (Fig. 5). Similarly, high colorectal cancer incidence rates among Koreans are also reported in the California Regional Cancer Registry. Recent rates of colorectal cancer among Korean immigrants living in that area have been approaching those recorded for Japanese and non-Hispanic whites [4].

All the data suggest that colorectal cancer is epidemic among Koreans, especially among the elderly. Environmental factors, characterized by a western lifestyle, seem to be closely related to the increased risk of colorectal cancer. Higher intakes of red and processed meat, a lack of physical activity, obesity, and alcohol drinking have been suggested to be risk factors for colorectal cancer in the numerous epidemiologic studies [5], while higher intakes of dietary fiber, green leafy vegetables, some micronutrients abundant in vegetables and fruits, such as folate, and calcium were reported to be protective factors. Because many diet- and lifestyle-related factors for colorectal cancer are modifiable, it is urgently needed to set up comprehensive primary prevention program against colorectal cancer to effectively cope with the rapidly increasing cancer in Korea. Several specific associations have also been observed between genetic polymorphisms and colorectal cancer. Moreover, environmental factors and related genetic predispositions have been reported to work in concert in colorectal cancer development. For example, the protective effect of the homozygous variant TT form of the methylenetetrahydrofolate reductase (MTHFR) C677T genotype on the risk of colorectal cancer seems to be modified by the level of methyl diets, i.e., by folate, which has a protective effect, or conversely by alcohol. Recommendation of higher intake of folate and lower intake of alcohol to the target population, especially those with TT genotype of MTHFR, may be an effective preventive approach against colorectal cancer [6]. Further studies are needed to clarify how these suggested environmental factors interact with genetic factors to modify the risk of colorectal cancer among Koreans and to develop more tailored preventive strategies applicable to Koreans.