Malignancy and metastasis
Causes and Symptoms (Magill’s Medical Guide, Sixth Edition)
Cancer cells are characterized by two primary features. One of these is uncontrolled cell division: Cells enter an unregulated, rapid growth phase by losing the controls that normally limit division rates to the amount required for normal growth and maintenance of body tissues. The second feature is metastasis, in which tumor cells lose the connections that normally hold them in place in body tissues, break loose, and spread from their original sites to lodge and grow in other body locations. Tumor cells with these characteristics are described as malignant.
The detrimental effects of solid malignant tumors result from the interference of rapidly growing masses of cancer cells with the activities of normal tissues and organs, or from the loss of vital functions because of the conversion of cells with essential functions to nonfunctional forms. Some malignant tumors of glandular tissue upset bodily functions by producing and secreting excessive quantities of hormones.
Solid malignant tumors, as they grow, compress surrounding normal tissues; they destroy normal structures by cutting off blood supplies and interrupting nerve function. They may also break through barriers that separate major body regions, such as internal membranes and epithelia or the gut wall. They may also break through the skin. Such breakthroughs cause internal or external bleeding and infection, and they destroy the organization and separation...
(The entire section is 1466 words.)
Treatment and Therapy (Magill’s Medical Guide, Sixth Edition)
Cancer is treated most frequently by one or a combination of three primary techniques: surgical removal of tumors, radiation therapy, and chemotherapy. Surgical removal is most effective if the growth has remained localized so that the entire tumor can be detected and removed. Often, surgery is combined with radiation or chemotherapy in an attempt to eliminate malignant cells that have broken loose from a primary tumor and lodged in other parts of the body. Surgical removal followed by chemotherapy is presently the most effective treatment for most forms of cancer, especially if the tumor is detected and removed before extensive metastasis has taken place. Most responsive to surgical treatments have been skin cancers, many of which are easily detected and remain localized and accessible.
Radiation therapy may be directed toward the destruction of a tumor in a specific body location. Alternatively, it may be used in whole-body exposure to kill cancer cells that have metastasized and lodged in many body regions. In either case, the method takes advantage of the destructive effects of radiation on DNA, particularly during periods when the DNA is under duplication. Because cancer cells undergo replication at higher rates than most other body cells, the technique is more selective for tumors than for normal tissues. The selection is only partial, however, so that body cells that divide rapidly, such as those of the blood,...
(The entire section is 1006 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Indications that malignancy and metastasis might have a basis in altered gene activity began to appear in the nineteenth century. In 1820, a British physician, Sir William Norris, noted that melanoma, a cancer involving pigmented skin cells, was especially prevalent in one family under study. More than forty kinds of cancer, including common types such as cancer of the breast and colon, have since been noticed to occur more frequently in some families than in others. Another indication that cancer has a basis in altered gene activity was the fact that the chromosomes of many tumor cells show abnormalities, such as extra chromosomes, broken chromosomes, or rearrangements of one kind or another. These abnormalities suggested that cancer might be induced by altered genes with activities related to cell division.
These indications were put on a firm basis by research with tumors caused by viruses infecting animal cells, most notably those caused by a group of viruses infecting mammals and other animals, the retroviruses. Many retroviral infections cause little or no damage to their hosts. Some, however, are associated with induction of cancer. (Another type of pathogenic retrovirus is responsible for acquired immunodeficiency syndrome, or AIDS.) The cancer-inducing types among the retroviruses were found to carry genes capable of transforming normal cells to the malignant state. The transforming genes were at first...
(The entire section is 526 words.)
For Further Information: (Magill’s Medical Guide, Sixth Edition)
Alberts, Bruce, et al. Molecular Biology of the Cell. 5th ed. New York: Garland, 2008. Describes the development and characteristics of malignance and metastasis. The text is clearly written at the college level and is illustrated by numerous diagrams and photographs.
Dollinger, Malin, et al. Everyone’s Guide to Cancer Therapy. 5th ed. Kansas City, Mo.: Andrews McMeel, 2008. An excellent source of medical information about cancer, written for the general public. Describes various cancer sites in the body. Includes a helpful glossary of medical terminology.
Eyre, Harmon J., Dianne Partie Lange, and Lois B. Morris. Informed Decisions: The Complete Book of Cancer Diagnosis, Treatment, and Recovery. 2d ed. Atlanta: American Cancer Society, 2002. This text from the American Cancer Society is intended for the layperson. It is exemplary in its discussion of cancer.
Lackie, J. M., and J. A. T. Dow, eds. The Dictionary of Cell and Molecular Biology. 4th ed. Boston: Academic Press, 2007. Encompasses cytology and molecular biology. Includes bibliographical references.
Lodish, Harvey, et al. Molecular Cell Biology. 6th ed. New York: W. H. Freeman, 2008. An excellent textbook written at the college level. Includes an unusually complete discussion of the characteristics and causes of malignancy and metastasis. Many highly illustrative diagrams and photographs are...
(The entire section is 297 words.)