Children, Cancer, and the Environment
Cancer is often described as being "genetic." However, this word can mean several different things.
People sometimes say cancer is "genetic" when they mean that children inherit traits that cause cancer from their parents. Children do inherit many traits from their parents through their genes. However, this can occur in two ways that are quite different.
In the first case, children may inherit a gene that has been present in their ancestors for generations. Such a gene would tend to affect several members of the family. The "breast cancer gene" is this type of a gene. Such inherited genes can be important cause of some forms of cancer. However, they appear to be the cause of a relatively small percentage of cancer cases. And for children, such genes are not a significant cause of cancer.
In the second case, a child may receive altered genes from their parents because of damage to the cells of the egg or sperm that merged during conception. Such damage may be caused by parents' exposures to environmental agents such as chemicals or radiation.
This often called a "germ line" mutation because the egg and sperm are considered to be "germ" cells. In this context, a germ cell is one from which all cells form and has nothing to do with the kinds of "germs" (like bacteria or viruses) that cause infectious diseases. Such germ line mutations may run in families because of similar environmental exposures. But the principal cause of the change is the environmental agent. Mutations of this type appear to be a more frequent cause of childhood cancer, particularly for very young children.
So, though much of cancer has a cause that is related to genetics, most cancer is also preventable. The factors that cause cancer are largely from sources outside the body and include so-called "lifestyle" factors as well as environmental agents such as chemicals and radiation and, in some cases, infectious agents (1, 2, 3).
Scientists are beginning to investigate the interaction between genes and the environment. In the past, scientists looked for genes that directly caused cancer and that could be found in families or they looked for chemicals that directly caused cancer. Now, scientists are beginning to understand that genetics and environmental factors have an interplay that varies among individuals and that may cause changes other than mutations.
Genetic factors influence how susceptible individuals are to carcinogens. There are also many ways that chemicals can disrupt the body. In addition to directly damaging DNA and causing a mutation, environmental agents may disrupt:
· The way that DNA provides signals to cells, telling them how to function;
· Cell growth
· The development of cells into specialized forms that are capable of performing specific tasks in the body
· Death of damaged cells
All of these are directed in some ways by DNA and so have a genetic component, but they also provide opportunities for interference by environmental agents.
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1. Perera FP, Weinstein IB. Molecular epidemiology: recent advances and future directions. Carcinogenesis 2000; 21:517-524.
2. Minamoto T, Mai M, Ronai Z. Environmental factors as regulators and effectors of multistep carcinogenesis. Carcinogenesis 1999; 20:519-27.
3. Lichtenstein P, Holm NV, Verkasalo PK, Iliadou A, Kaprio J, Koskenvuo M, Pukkala E, Skytthe A, Hemminki K. Environmental and heritable factors in the causation of cancer--analyses of cohorts of twins from Sweden, Denmark, and Finland. New England Journal of Medicine 2000; 343:78-85.
