Has anyone you know had cancer?
If so, what type of cancer was it? What were its symptoms? Based on the information presented so far in this chapter, did the person have any of the known risk factors for the disease?
Lymphoma is a form of cancer that begins in the lymph nodes and then may spread to almost any part of the body. There are two types Hodgkin’s disease and non-Hodgkin’s lymphoma (NHL). NHL is the more common and more deadly form of the disease. Risk factors for NHL are not well understood but may include genetic factors, radiation, and certain chemicals and infections.
THE CAUSES OF CANCER
Although scientists do not know everything about what causes cancer, they have identified genetic, environmental, and lifestyle factors. Rates of cancer have declined among all U.S. ethnic groups in recent years, but significant disparities still exist. For example, genetic factors may help explain the high rate of prostate cancer among black men. Cultural factors may explain why women belonging to social groups that encourage early marriage and motherhood are likely to have a lower risk of breast cancer. People with low incomes and a lack of health insurance have higher cancer death rates.
The Role of DNA
Heredity and genetics are important factors in a person’s risk of cancer. Certain genes may predispose some people to cancer, and specific gene mutations have been associated with cancer.
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DNA Basics The nucleus of each cell in your body contains 23 pairs of chromosomes, which are made up of tightly packed coils of DNA (deoxyribonucleic acid). Each chromosome contains hundreds or thousands of genes; you have about 25,000 genes in all. Each of your genes controls the production of a particular protein. By making different proteins at different times, genes can act as switches to alter the ways a cell works. Some genes are responsible for controlling the rate of cell division, and these genes often play a critical role in the development of cancer.
DNA Mutations and Cancer A mutation is any change in the makeup of a gene. Some mutations are inherited; others are caused by environmental agents known as mutagens. Mutagens include radiation, certain viruses, and chemical substances in the air we breathe. (When a mutagen also causes cancer, it is called a carcinogen.) Some mutations are the result of copying errors that occur when DNA replicates itself as part of cell division.
A mutated gene no longer contains the proper code for producing its protein. It usually takes several mutational changes before a normal cell takes on the properties of a cancer cell. Genes that have mutations associated with the conversion of a normal cell into a cancer cell are known as oncogenes. In their undamaged form, many oncogenes play a role in controlling or restricting cell growth; they are called tumor suppressor genes. Mutational damage to suppressor genes releases the brake on growth and leads to rapid and uncontrolled cell division a precondition for the development of cancer.
An example of an inherited mutated oncogene is BRCA1 (breast cancer gene 1). Women who inherit a damaged copy of this suppressor gene face a significantly increased risk of breast and ovarian cancer.
In most cases, however, mutational damage occurs after birth. For example, only about 5-10% of breast cancer cases can be traced to inherited copies of a damaged BRCA1 gene. In addition, lifestyle factors are important even for those who have inherited a damaged suppressor gene. Testing and identification of hereditary cancer risks can be helpful for some people, especially if it leads to increased attention to controllable risk factors and better medical screening.
Cancer Promoters Substances known as cancer promoters make up another important piece of the cancer puzzle. These substances don’t directly produce DNA mutations, but they accelerate the growth of cells, which means less time for a cell to repair DNA damage caused by other factors. Estrogen, which stimulates cellular growth in the female reproductive organs, is an example of a cancer promoter.
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