Man’s running battle with carcinogens

Press, Volume CXVI, Issue 34047, 10 January 1976, Page 10

Man’s running battle with carcinogens

JANE BRODY of the “New York Times” reviews a very unpleasant subject.

Hardly a week goes by without a new report that some previously unsuspected substance has been found to cause cancer.

Thus far, the scientists have pinpointed more than 1000 agents as definite or suspected causes of cancer in man. In recent years, such agents — called carcinogens — have been discovered in the air we breathe, the water we drink, the foods we eat, the clothes we wear, the drugs we take, the jobs we hold, the habits we pursue.

Recently three new reports were released on cancer causes — one stating that a number of common cancers may be caused, directly or indirectly, by ordinary components of the daily diet, a second linking the use of estroagens during and after the menopause to an increased risk of developing uterine cancer, and a third describing a high rate of skin cancer among workers who produce synthetic fuels. Such reports are apt to confuse many people, including doctors, who wonder what they will

next have to give up if they want to protect themselves from the scourge of malignancy. Indeed, in the face of such a long list of can-cer-causing agents, many people are inclined to think that almost everything causes cancer and that they might as well resign themselves to the fact that there is no way to prevent exposure to such a broad spectrum of carcinogens.

If nothing else, the reports illustrate that cancer is an extremely complex disease. In fact, although a single word is used to describe it, cancer is really at least 100 different diseases. Furthermore, any one form of cancer may be caused by a number of factors working alone or in concert, directly or indirectly For example, in the report on nutritional factors in cancer, diets high in animal fat (such as the typical American diet) were associated with an increased risk of developing cancers of the

colon and breast. Fats in the diet do not appear to change cells directly from normal to cancerous. Rather, the fats are believed to change the metabolism in ways that render organs like to colon and breast more susceptible to cancer. Yet, even if a fatty diet is only an indirect cause of cancer, a change in that diet would lower a person’s cancer risk. The newly-discovered link between estrogens and cancer of the endometrium, or lining of the uterus, is like the fatty diet link, a statistical one, although here the evidence suggests a direct carcinogenic effect of the hormones on a sensitive organ.

Some suspected cancercausing agents — such as the artificial sweetner, cyclamates — have indicated possible carcinogenic potential only in animal tests. A few substances, such as the ingredients of hair dyes, are thought to have cancer-causing ability on the basis of tests

on bacteria. But vinyl chloride, the plastics chemical, has thus far been associated with 45 cases of a fatal liver cancer among exposed workers and has been clearly established through human and animal studies as a definite cause of cancer in man. It has also been shown that susceptibility to different carcinogens can vary greatly from one person to another. Such factors as a person’s genetic predisposition, age, sex, immunologic responsiveness and perhaps even psychological state may modify the effect of a carcinogen, resulting in cancer in one person while another individual similarly exposed to the agent remains healthy. For example, at a conference on the genetic aspects of cancer, a survey

of 5000 people was described. It showed that, on a routine check-up, nearly 10 per cent of those who had a parent or sibling with cancer were also found to have cancer. If two immediate relatives had cancer, risk was 16 per cent, and it jumped to 22 per cent — more than one in five — for persons with three or more cancer victims among their close relatives.

Carcinogenic substances may also interreact with one another or with certain viruses to cause a cancer that one substance alone could not produce. Although there is an intense search going on for human cancer viruses, none has been identified, and most cancer specialists, including some virologists, are looking more and more to environmeri-

tai factors as the most important causes of cancer in man.

The three American winners of the 1975 Nobel Prize in medicine, who were honoured for their discoveries involving cancer viruses, blamed outside environmental factors for causing up to 80 per cent of cancers in man. The Nobel laureates, Drs David Baltimore, Howard Temin and Renato Dulbecco, said that about half of the cancers from these factors could be eliminated — especially those related to cigarette smoking, the most prominent environmental cancer cause — but that the public appeared to turn its back on expert advice.

In today’s complex society, there are hundreds of thousands of manmade substances, many of which may be inimical to the human body. As Dr Gio Gori, or the National Cancer Institute, said in a report on nutrition and cancer,

today’s diet probably is biologically ' disadvantageous. “From an evolutionary point of view,” he said, “modem man is still outfitted with a body that over millions of years has adapted to Stone Age conditions, when the foods available were very different from our modern diet and the caloric comsumption probably far exceeded the demands of our sedentary habits.” Similarly, adaptability of the human body is probably being overwhelmed with other earmarks of progress, and environmentally caused cancers may be the price for certain “luxuries.”

For example, women who once had to put up with the discomforts of menopause now can take estrogens, which are effective in relieving these symptoms — but which may cause cancer. The mere fact that other causes of death have been conquered, greatly reducing mortality before middle age, means

that most leople are now living to he older ages when canct becomes far more commtn. Identificatbn of environmental carcinogens helps society to decide what trade-ofs to make in the name o progress. Knowing the risks helps in findhg ways to avoid some aid to min imise others. Another form of homhne treatment may be just as effective as esfrogens in controlling rnenopausa! symptoms but without creating a risk tf cancer. Or persons gmetically predisposed to cancer may be advised to restrict their exposure to certain agents. Or exposed people pay be monitored periodfcally to detect reversibh precancerous changes. It seems, however, that we may have to ive with some cancer risks if the benefits derived from the condition that Itada to those risks — or the costs of eliminating the risks — are sufficient] v great.