Carcinogens

Cancer is a series of diseases characterized by abnormal cell growth and spread of cancerous cells through the body. A carcinogen is a substance that can cause cancer in humans or animals. Sometimes substances promote cancer or aggravate cancers but do not cause them. These substances also may be called carcinogens. Carcinogens include both naturally occurring substances (radon gas) and substances created as a result of production (the components of tobacco). Lists of known carcinogens are maintained by national and world agencies, such as the National Cancer Institute, the International Agency for Research on Cancer, the National Toxicology Program, and the World Health Organization.

Geographers have been involved in the study of cancer because there are obvious geographical differences between nations, within states and provinces in the same nation, among adjacent local governments, and even within neighborhoods. This entry highlights several of the most important contributions made by epidemiologists and geographers.

At the international and intranational scales, researchers have gained important insights about carcinogens by comparing the cancer incidence and mortality rates of immigrants. For example, a Polish epidemiologist compared cancer rates of Polish citizens who lived in Poland, Polish migrants to the United States, and the progeny of Polish migrants who lived in the United States. Residents of Poland had notably higher stomach cancer rates than the progeny of Polish migrants to the United States. Migrant studies are not confined to international comparisons. For instance, within the United States, the cancer death rates of Southern-born African Americans were compared with those of their counterparts born elsewhere in the United States. Southern-born African Americans had higher digestive, urinary, and respiratory cancer rates, irrespective of whether they lived in the South or had migrated to other locations in the United States.

Migrant studies such as these provide clues to field- and laboratory-based cancer researchers, allowing them to investigate the reasons for the different rates. For example, investigators [Page 336]studied the food preferences and eating habits of African Americans residing in Harlem in New York City who were born in the Northeast, in the South, and in the Caribbean and found marked differences in their food preparation and consumption patterns. The United States has experienced a substantial increase in immigration in places such as California, New York, and New Jersey, and these places are rich environments for cancer-oriented migrant studies. These so-called migrant studies are inherently geographical and appeal to those who are interested in the study of risk factors for cancer, including food preferences, cooking and food preservation practices, tobacco and alcohol use, workplace exposures, and many others.

A second important area of cancer research that geographers have contributed to is cancer cluster investigations. Every year, residents of some neighborhoods report that there are an excessive number of cancers in their communities. To verify that a cluster exists, scientists must review every case, map the data, and compare the cancer cases with the number expected by chance. If there is indeed an excess, then public health experts will try to understand why the rates are higher than expected. Typically, no cause can be found, leading often to considerable public angst.

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