July 28, 2000 (Ira Pilgrim)

Mutations and Cancer

Fear not the atom in fission;

The cradle will outwit the hearse;

Man on this earth has a mission--

To survive and go on getting worse.

Samuel Hoffenstein, 1947

The same process is involved in the production of changes in genes(mutation) and the production of cancer(carcinogenesis). Things that cause mutations can also cause cancer, and they do. It is possible that mutations happen on their own in the process of cell division. Still, most of what we understand about the process of mutation probably involves the action of ionizing radiation or chemicals. It is possible that what will cause a cancer in one organ may not cause it in another. In this column, I will use the words "may" and "might" fairly frequently because our understanding of what happens is far from complete.

The process that is best understood involves ionizing radiation, which, unlike heat or visible light radiation, will disrupt atoms and molecules, including DNA, which is the gene. When a gene is changed, it is often repaired; but not often enough. If a gene that is essential to life is changed, the cell dies. This is no problem because there are lots more cells where that came from. If it happens to be a nerve cell in the adult brain, it will probably not be replaced. If the mutation occurs in one of many genes that regulate the multiplication of cells and growth, it might produce a tumor or a cancer. A cancer is a tumor(lump) that does not stop growing and may spread to parts of the body where it doesn't belong.

Before Roentgen discovered x-ray, all of the ionizing radiation that people were exposed to came from the decay of natural radioactive substances in the Earth, and from the Sun. The Sun puts out a large amount of ionizing radiation. The best known is ultraviolet light(UV). UV only penetrates a small distance into the skin where it can cause sunburn, skin cancer and melanoma(a cancer of the pigment cells). Other kinds of ionizing radiation such as x-rays can penetrate into much deeper layers of the body, where they can cause mutations and cancer. If the mutation occurs in a sperm producing cell or an egg, it can cause the death of the embryo or some abnormality in the child. As a consequence, increasing the amount of radiation that people are exposed to can be responsible for a hellofalot of human misery.

Ionizing radiation cannot be felt unless you get a hefty dose. Ultraviolet radiation can causes sunburn if you get enough of it. Large amounts of x-ray can burn skin as well as destroy cells deep inside the body. Most of the time, the radiation or chemicals that cause mutations can not be felt. Consequently, people do not associate the mutagen with the cancer that occurs much later, nor with the abnormality that occurs in a child. Usually the cancer or abnormality occurs many years after the radiation or chemical impinged on an individual. It is hard to see how a fluoroscopic examination that an infant had can cause breast cancer when that individual is in her/his fifties. Yet that is what actually happens. It is not possible to predict precisely what an event like the Chernobyl disaster will have on the population of the world. We can say with certainty that it will cause cancer and gene mutation, and that the greater the exposure to the radiation, the greater the effect, but it is impossible to put reliable numbers on how many cancers will be produced. People who are in the x-ray or nuclear power plant business tend to downplay the effect.

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