Research Contributions from Earlier Atlases

The Atlas of Cancer Mortality in the United States, 1950-94 is a continuation of the cancer mapping project in the National Cancer Institute's (NCI's) epidemiology program. The first atlas of color-coded mortality maps at the county level was published in 1975 and covered the 20-year period from 1950-69. By using county rates, the maps made it possible to uncover patterns of cancer that previously had escaped notice when larger areas, such as states, were mapped.

The color maps in the first atlas revealed a surprising number and variety of geographic patterns, made it easy to see clustering of high-rate areas, and stimulated scientists to look for causes of the elevated rates. A series of additional cancer atlases, plus an atlas on other causes of death, have been published since then. (Consult the new atlas for a list of these references.)

It often requires many years of work, however, to uncover the reasons for the geographic variation in mortality for a specific cancer. At NCI, scientists have launched several descriptive and correlational studies to characterize the rates in more detail and generate hypotheses about possible risk factors. Possible risk factors include tobacco use, occupational exposures, dietary habits, ethnic background, and environmental exposures from the air or water. These studies have been helpful in developing leads for more in-depth studies.

To test their hypotheses, researchers conduct field studies in high-rate areas to see if a particular exposure is associated with an increased risk and, if so, to what extent. Individuals with and without the particular cancer are interviewed in an effort to uncover environmental or lifestyle factors that might be responsible for the high rates. These studies often take four to five years to conduct and publish.

Several correlation and field studies were stimulated by the publication of previous atlases. The conclusions from some are listed below.

General findings

• Variations in cigarette smoking greatly influence the patterns of lung and certain other tobacco-related cancers (larynx, esophagus, and oral cavity).

• The patterns of alcohol consumption contribute to the geographic variation for cancers of the oral cavity and pharynx, esophagus, and larynx.

• Dietary factors, including the protective effects of fruit and vegetable consumption, may influence the patterns of esophageal, stomach, colorectal, and other cancers.

• Infectious agents may contribute to the variation in rates seen for several cancers; these include human papillomavirus (cervical cancer), hepatitis B and C (liver cancer), Helicobactor pylori (stomach cancer), human immunodeficiency virus (HIV), and Epstein-Barr virus (lymphomas).

• Occupational exposures are implicated in areas with elevated rates for cancers of the lung (smelter workers exposed to inorganic arsenic and shipyard workers exposed to asbestos), nasal cavity (furniture workers), bladder (truck drivers), and possibly lymphoma (farmers).

Oral and pharyngeal (throat) cancers

• Cigarette smoking and alcohol consumption, the dominant risk factors for these cancers, contribute to the geographic patterns observed.

• Use of smokeless tobacco in the form of snuff dipping (placing ground or powdered tobacco in the mouth) is the primary reason for elevated mortality rates from mouth and throat cancers among women in the rural Southeast.

• Fruit and vegetable intake protects against tobacco-related oral cancers.

Esophageal cancer

• In Washington, D.C., and coastal areas of South Carolina, high rates of esophageal cancer reflect strong associations with alcohol consumption and tobacco use, along with deficiencies in fruit and vegetable consumption.

• Heavy use of home-brewed whiskeys among black men in the South Carolina low country appear to be partly responsible for the elevated rates in that area.

Stomach cancer

• Elevated rates among whites in the Southwest appear to reflect excess risk among Hispanics, while elevated rates in the north central areas appear to be related to the concentration of Scandinavian and other high-risk ethnic groups from Europe.

• In high-risk areas of south Louisiana, studies suggest protective effects for fruit and vitamin C consumption in whites and blacks, while consumption of smoked food and home-cured meats are associated with increased risk among blacks, but not whites.

• There is mounting evidence that infection with Helicobactor pylori, particularly at young ages, plays a key role in the development of stomach cancer; little is known about the geographic distribution of the prevalence of infection in the United States.

Colon cancer

• High colon cancer death rates in eastern Nebraska are linked to persons of Czechoslovakian background, and nutritional factors appear to contribute to the elevated risk.

Pancreatic cancer

• High rates of pancreatic cancer in southern Louisiana are associated with cigarette smoking and with dietary habits characteristic of the Cajun population, especially the use of pork products and low fruit consumption.

Nasal cancer

• Elevated rates of nasal cancers are found among men in counties with a high proportion of furniture-industry employees as well as textile workers.

Lung cancer

• Cigarette smoking is the dominant cause of lung cancer in the United States, and smoking patterns largely account for the regional variation in lung cancer mortality rates.

• Exposure of workers to asbestos in the shipbuilding industry, particularly those who worked there before 1949, contribute to the elevated lung cancer mortality rates seen in coastal areas of Georgia, Virginia, northeastern Florida, and Louisiana.

• Smoking habits, including the use of hand-rolled cigarettes, also contribute to the elevated lung cancer mortality rates seen among Cajuns in southern Louisiana.

• Studies also show elevated rates of lung cancer among men and women residing in counties with arsenic-emitting smelters.

Melanoma and other skin cancer

• Exposure to ultraviolet radiation from sunlight, especially at a young age, accounts for consistently higher levels of melanoma and other skin cancers seen in the South, as compared to the northern parts of the country.

Breast cancer

• Death rates for breast cancer have been elevated among women in areas of the Northeast for over four decades.

• Regional variation in breast cancer rates are partially attributed to the distribution of established risk factors, including late age at first birth, early menarche, and late menopause, as well as other factors, such as education and mammography history.

• Little geographic variation in mortality is seen for premenopausal women.

Cervical cancer

• The geographic, racial, and socioeconomic patterns of cervical cancer mortality are mainly to variations in the prevalence of human papillomavirus and the use of Pap smears to detect premalignant lesions, which can then be cured.

Prostate cancer

• There is some evidence that farming and agricultural exposures may contribute to the geographic variation in prostate cancer, including high rates among whites in north central and northwestern areas, and among blacks in parts of the Southeast.

Bladder cancer

• Bladder cancer among men has clustered in the urban Northeast since the 1950s, particularly in areas with chemical industries.

• Increased risk of bladder cancer is seen among truck drivers and other workers exposed to motor exhausts.

• Cigarette smoking accounts for one-half of bladder cancer cases.

• High rates have persisted among men and women in parts of the Northeast, especially in northern New England, prompting new studies to elucidate reasons for this unusual pattern.

Non-Hodgkin's lymphoma

• A recent correlation study suggests no link between non-Hodgkin's lymphoma and sunlight exposure, in contrast to some earlier studies.

• There is a link between pesticide use by men in central areas of the country and non-Hodgkin's lymphoma.

• New studies are attempting to clarify reasons for the upward trend in the incidence of this cancer.

Multiple myeloma

• Elevated rates seen in the black population are at least partly due to socioeconomic factors.

Leukemia

• Some studies suggest that pesticides and other agricultural exposures may contribute to the geographic variation in leukemia. High rates among white men and women occur in a central band of the country from the plains states to the Midwest and south to the Gulf coast, along with a scattering of high rates in the East and West.