Ma and Yu: Global Burden of Cancer 91 [11]. For example, Helicobacter pylori in- fection is known to increase the risk of stom- ach cancer [12], whereas infection with hepatitis B and C viruses can lead to liver cancer [13]. The relationship between so- cioeconomic status and the acquisition of Helicobacter pylori infection has been con- firmed in a number of studies; the preva- lence of infection varies from 8.9 percent to 72.8 percent among children from devel- oped and developing countries, respectively; the re-infection rate is also significantly higher in the latter [14]. Similarly, the preva- lence of infection with hepatitis B and C viruses is higher in developing countries than in developed countries [15]. The higher incidences of stomach and liver cancers in developing countries are largely due to the higher prevalence of related infections. Other infections considered to be important in cancer include human papilloma virus, Epstein-Barr virus, and human immunode- ficiency virus [11]. Diet and physical activity Excessive weight and obesity, resulting from excess calorie intake and physical inac- tivity, have become a serious health issue in many developed countries. In the United States, for example, it is estimated that nearly a third of the adult population is obese and two-thirds are overweight [16]. Obesity and excessive weight have been linked to many types of cancers, including those of the colon, breast, and prostate [17]. The higher incidences of colon, breast, and prostate cancers in developed countries are attributed in part to a lifestyle of high-calorie diet and physical inactivity. This lifestyle re- sults in positive energy imbalance that fur- ther leads to insulin resistance (or metabolic syndrome) characterized by hyperinsuline- mia, dyslipidemia, hypertension, and glu- cose intolerance [18]. Insulin resistance has been linked to a number of health problems including cancer, type 2 diabetes, and car- diovascular diseases [19]. These lifestyle-re- lated health issues have begun to spread to certain developing countries where there has been steady economic growth. This spread also results in changes in regional cancer patterns. For example, dramatic increases in the incidences of breast, prostate, and colon cancers have been observed in the major cities of China [20]. MORTALITY OF CANCER BY GEOGRAPHIC REGIONS In 2002, Asia had the largest number of cancer deaths in the world, a total of 3,355,928 deaths, including 1,983,473 males and 1,372,455 females, followed by Europe (1,701,472), and North America (631,971). The mortality of cancer also increased dra- matically with age for both males and fe- males (Table 3-4). For males, the highest age-standardized mortality rate was ob- served in Eastern Europe (197.2 per 100,000 person-years) and the lowest in Western Africa (73.5 per 100,000 person-years). The geographic variation in cancer mortality was not as substantial as the geographic variation in cancer incidence. More developed regions such as North America had relatively low cancer mortality despite having high cancer incidence. On the other hand, some less de- veloped regions had relatively high cancer mortality despite having low cancer inci- dence. This disparity is clearly shown in Fig- ure 4 — the gap between incidence and mortality in males was larger in more devel- oped countries than in less developed coun- tries. There was a similar pattern in females (data not shown). The disparity could be due to the different profiles of cancer in more or less developed countries. For example, prostate cancer is common in more devel- oped countries, and it is usually associated with a fairly good prognosis and does not have a severe impact on survival. The dis- parity also could be due to the resources available for the screening and treatment of cancer in more or less developed countries. For example, the incidence rates of female breast cancer were nearly three-fold higher in more-developed than less-developed countries; whereas, mortality rates were less than two-fold higher in more-developed than less-developed countries. Conse- quently, the mortality/incidence rate ratio varied widely, from a low of 0.19 in North