Scientists do not fully understand the causes of cancer, but studies show that some people are more likely to develop the disease than others. The incidence of cancer varies enormously among different regions.
The highest death rate from all cancers in males is 272 per 100,000 men in Hungary while the lowest death rate of 80 men per 100,000 is found in Mauritius, an island off the coast of eastern Africa. For women the highest cancer rate is 140 per 100,000 women in Denmark compared to only 63 per 100,000 women in Azerbaijan in western Asia. The figures for the United States are 156 per 100,000 men and 108 per 100,000 women. For particular cancers, the difference between countries may be as high as 40-fold. Differences also occur within populations. Cancer rates vary between sexes, races, and socioeconomic groups, for example. Scientists called epidemiologists study particular populations to identify why cancer rates vary. One method they use is to compare behavior and characteristics such as the gender, age, diet, or race of cancer patients to those of healthy people. Population studies provide useful information about risk factors that increase the likelihood of developing cancer.