Geography and cancer
Geography and cancer is a field that examines how the incidence and mortality rates of various cancers differ across regions and populations globally. The distribution of cancer is not uniform; while industrialized nations report higher incidence rates, developing countries often see more deaths from the disease. For example, about 70% of annual cancer-related deaths occur in developing nations. Factors influencing cancer patterns include gender, ethnicity, socioeconomic status, and urban versus rural living conditions.
Common types of cancer examined include lung, breast, colorectal, and prostate cancers, each displaying unique geographical trends. Lung cancer, for instance, has significant variations in incidence rates, affected by risk factors like smoking and air pollution. Other cancers, such as esophageal and stomach cancer, demonstrate marked geographical disparities—esophageal cancer is notably prevalent in Eastern Asia, while stomach cancer is concentrated in East Asia and Central Europe.
Breast cancer is the most common cancer among women, with the highest rates found in North America and Europe. Additionally, socio-economic barriers in developing countries contribute to higher mortality rates from cervical cancer and other reproductive system cancers, underscoring the need for improved healthcare access and education. Understanding these geographical patterns aids in addressing cancer prevention and control strategies appropriate to diverse populations.
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Subject Terms
Geography and cancer
DEFINITION: Cancer geography is concerned with the geographic distribution of various forms of the disease. Mapping the location of cancer incidence and identifying things like cancer clustering aims to improve the understanding of the multiple factors that affect human health. It is akin to epidemiology, studying population causes, distribution, and disease control.
Cancer and world populations: Cancer affects populations differently in various parts of the world. Though incidence rates are higher in industrialized nations, developing nations experience a higher incidence of death from cancer. Annually, around 70 percent of the ten million cancer-related deaths occur in developing nations. Cancer incidence may differ among regions in a given country or between populations in geographically separated countries. Several factors contribute to identifying how particular kinds of cancer affect populations. Certain cancers may occur in differing patterns between men and women, White or Black populations, northern or southern areas, urban or rural groups, poor or affluent populations, Western or Eastern peoples, developed or developing countries, and among ethnic subgroups. The most common cancers include breast, lung, colorectal, and prostate cancers. Reporting of cancer incidence is typically made as age-standardized incidence rates per 100,000 persons.
Lung cancer: Worldwide, lung cancer is one of the most often diagnosed and most deadly cancers. In the United States, around 17 percent of lung cancer patients survive five years after diagnosis. International variations in lung cancer incidence are vast, from an incidence rate of up to 130 per 100,000 people in developing nations to over 300 per 100,000 in industrialized countries. The most significant risk factors are cigarette smoking, atomic radiation, and air pollution, which are geography-associated risks. The incidence of lung cancer is higher worldwide among men than women and rises sharply with age. Among men, lung cancer incidence rates in Middle Eastern populations are much lower than in Western populations.
Cancers of the digestive tract: Worldwide, esophageal cancer appears most often in Eastern Asia and Southern and Eastern Africa at an average rate of 6.3 per 100,000 individuals. The geographical differences in the incidences of esophageal cancer are more marked than for any other type of cancer. One especially high-risk area ranges from northern Iran to north-central China and consequently has been labeled the “esophageal cancer belt.” However, the incidence rate of esophageal cancer in nearby countries, such as Syria, Jordan, and Israel, is among the lowest worldwide, possibly attributable to low levels of alcohol consumption. However, these same countries have a high prevalence of smoking, a significant risk factor. Worldwide, incidence rates are higher in men than women, increasing with age. In the United States, adenocarcinoma is the most common type. About 95 percent of all esophageal cancer in the rest of the world is squamous cell carcinoma. In England, esophageal cancer is found more often in rural than in urban areas, but the opposite is true in Denmark. The global incidence rate of esophageal cancer increased by 94.7 percent from 1990 to 2020.
The incidence of stomach cancer, also called gastric cancer, ranks among the most common and deadly cancers. The areas of highest risk are East Asia and Central and Eastern Europe. About 45 percent of stomach cancer cases occur in China. Laborers in Sumatra, an Indonesian island in East Asia, have a high rate of both stomach and liver cancer. Still, Japanese laborers who work alongside Chinese workers have almost no stomach cancer, though they, too, have a high liver cancer rate. Second-generation immigrants who come from high- to low-risk areas are less likely to develop stomach cancer than were their parents.
Globally, the incidence rate for colorectal cancer is about 20 per 100,000 men and 15 per 100,000 women. However, this cancer is much more common in the Western world, with higher incidence and mortality (incidence rates in Australia/New Zealand are 44.8 per 100,000 in men and more than 32.2 per 100,000 in women), while the incidence rates are only about 5 per 100,000 for and women in western Africa. Migrants from low-risk areas to high-risk Western countries experience a rapid increase in colorectal cancer risk within a generation, possibly because of changes in dietary habits. Low red meat and dietary fat consumption in Asia and Africa play a role in the low incidence. Some studies suggest that tobacco and alcohol use may also play a role. Genetic risk factors have also been identified. For example, Ashkenazi and Israeli Ashkenazi Jews (Jews of European origin) have a significantly increased risk of having colorectal cancer. The low incidence in some areas, such as Egypt, could be because of low detection rates or local protective nutritional factors.
Incidence of pancreatic cancer ranks twelfth worldwide, but this cancer ranks considerably higher in its mortality rate, partly because of late diagnosis. The highest incidence is in African American men (16.2) and Hawaiians (12.3), but there are also high rates among Korean, Czech, Latvian, and New Zealand Maori men. The Scandinavian countries have the highest incidence rates in Europe. In some areas, notably India, pancreatic cancer is rare.
Kidney and urinary tract cancer:Kidney cancer is found mainly among White populations from developed countries in which risk factors are unusually prevalent. Worldwide, the Czech Republic has the highest incidence rate of 24.1 per 100,000 in men, Lithuania, Estonia, Slovakia, Latvia, and the United States. Generally, rates are considerably lower in Asian, African, and some South American countries.
The bladder is one of the most common sites of cancer worldwide, but the highest incidence is in industrialized countries. Incidence rates of more than 40 per 100,000 have appeared in Europe, notably in Belgium and Italy. The rate in the United States and Canada is about half of that in Europe. The lowest incidence rates are in Asia and South America. More men than women develop bladder cancer, but the geographical pattern for women is the same as for men.
Breast cancer: Globally, breast cancer is the second leading cause of death in women. It is the most common cancer among women, excluding nonmelanoma skin cancer. The incidence is highest in North America and Europe and lowest in Africa. In the United States, the number of new cases for women is much higher in some states.
Cancers of reproductive system organs: Cervical cancer is the fourth most common cancer among women, and it is much more common in developing countries, with nearly 85 percent of new cases and 90 percent of cervical cancer deaths occurring in developing nations. Research suggests differences in incidence are attributable to socioeconomic factors. Screening programs, vaccines for human papillomavirus (HPV) infections, education, and early treatment measures are lacking in developing nations, leading to hundreds of thousands of preventable deaths each year.
Uterine cancer, also called corpus (body of the uterus rather than the mouth or cervix) or endometrial cancer, has a distribution pattern similar to that of ovarian cancer. High incidence appears in North America and Eastern Europe.
Much research indicates that ovarian cancer occurs more often among middle- and upper-class women from industrialized nations, especially those in Western and northern Europe and North America, and is uncommon in less-developed countries. Among cases diagnosed in Middle Eastern countries, female Israeli Jews have the highest incidence rate. One possible explanation is differing dietary factors. The majority of ovarian cancers are diagnosed at an advanced stage because few symptoms are visible in the early stages. Although there are several risk factors, those related to geography are being White (although some studies maintain that race is not a factor) and living in a sunlight-deficient area (with consequent deficiency in vitamin D). Generally, the higher the latitude, the higher the risk. For example, at one point, the incidence in Iceland and Norway was about five times that in equatorial regions such as Asia, South America, and Africa.
Prostate cancer is the second most prevalent cancer among men, especially in Western countries such as Norway, Sweden, and the United States. There is marked variation in incidence worldwide, with a ratio of 1:100 between low- and high-incidence countries. The lowest rates are found in parts of China and other Asian countries. Genetic factors may explain some of the geographical variation.
Thyroid cancer: Although the incidence of endocrine gland malignancies, such as thyroid cancer, is relatively low worldwide, the rate has been on the increase for several decades. Thyroid cancer is more common among American women than men and is the fastest-growing cancer in the United States. In the Middle East, the rates are highest for Israeli Jews and lowest for Egyptians. The primary risk factor for the most common types is radiation exposure in childhood. Thus, survivors of the Japanese atomic bombings, those exposed to radioactive fallout in the Chornobyl disaster in Ukraine, and people exposed to radiation from nuclear testing account for geographical differences in the incidence rates. Follicular thyroid cancer incidence is related to iodine deficiency and endemic goiter. However, an iodine-rich diet may be associated with a higher incidence of the papillary type of cancer.
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