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Animal Cancer Tests

Animal cancer tests


Cancer causes more loss of life-years than any other disease in the United States. At first reading, this statement seems to be in error. Does not cardiovascular disease cause more deaths? The answer to that rhetorical question is "yes." However, many deaths from heart attack and stroke occur in the elderly. The loss of life-years of an 85 year old person (whose life expectancy at the time of his/her birth was between 55 and 60) is, of course, zero. However, the loss of life-years of a child of 10 who dies of a pediatric leukemia is between 65 to 70 years. This comparison of youth with the elderly is not meant in any way to demean the value that reasonable people place on the lives of the elderly. Rather, the comparison is made to emphasize the great loss of life due to malignant tumors.

The chemical causation of cancer is not a simple process. Many, perhaps most, chemical carcinogens do not in their usual condition have the potency to cause cancer. The non-cancer causing form of the chemical is called a "procarcinogen." Procarcinogens are frequently complex organic compounds that the human body attempts to dispose of when ingested. Hepatic enzymes chemically change the pro-carcinogen in several steps to yield a chemical that is more easily excreted. The chemical changes result in modification of the procarcinogen (with no cancer forming ability) to the ultimate carcinogen (with cancer causing competence). Ultimate carcinogens have been shown to have a great affinity for DNA, RNA, and cellular proteins, and it is the interaction of the ultimate carcinogen with the cell macromolecules that causes cancer. It is unfortunate indeed that one cannot look at the chemical structure of a potential carcinogen and predict whether or not it will cause cancer. There is no computer program that will predict what hepatic enzymes will do to procarcinogens and how the metabolized end product(s) will interact with cells.

Great strides have been made in the development of chemotherapeutic agents designed to cure cancer. The drugs have significant efficacy with certain cancers (these include but are not limited to pediatric acute lymphocytic leukemia, choriocarcinoma, Hodgkin's disease, and testicular cancer), and some treated patients attain a normal life span. While this development is heartening, the cancers listed are, for the most part, relatively infrequent. More common cancers such as colorectal carcinoma, lung cancer, breast cancer, and ovarian cancer remain intractable with regard to treatment.

These several reasons are why animal testing is used in cancer research. The majority of Americans support the effort of the biomedical community to use animals to identify potential carcinogens with the hope that such knowledge will lead to a reduction of cancer prevalence. Similarly, they support efforts to develop more effective chemotherapy. Animals are used under terms of the Animal Welfare Act of 1966 and its several amendments. The act designates that the U. S. Department of Agriculture is responsible for the humane care and handling of warm-blooded and other animals used for biomedical research. The act also calls for inspection of research facilities to insure that adequate food, housing, and care are provided. It is the belief of many that the constraints of the current law have enhanced the quality of biomedical research. Poorly maintained animals do not provide quality research. The law also has enhanced the care of animals used in cancer research.

[Robert G. McKinnell ]

RESOURCES

PERIODICALS


Abelson, P. H. "Tesing for Carcinogens With Rodents." Science 249 (21 September 1990): 1357.

Donnelly, S., and K. Nolan. "Animals, Science, and Ethics." Hastings Center Report 20 (May-June 1990): suppl 1l32.

Marx, J. "Animal Carcinogen Testing Challenged: Bruce Ames Has Stirred Up the Cancer Research Community." Science 250 (9 November 1990): 7435.

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