Scientists Know Cancer’s Cause, but Not Its Why
A factory worker is suing his employer, a saccharin manufacturer, claiming he developed lung cancer in 1986 as a result of inhaling artificial sweetener dust over a 12-year period.
The plaintiff, Robert Hamilton, 62, has charged the company ignored safety standards and allowed virtual clouds of a known cancer-causing agent to pervade the plant.
The company, Alberto-Culver Co., of Melrose Park, Ill., argues that Hamilton’s lung cancer was not caused by saccharin at all, but rather by his reputed pack-a-day smoking habit stretching from the 1960s to 1981.
The 1987 lawsuit, if and when it finally makes it to court, will undoubtedly raise interesting legal questions.
But the scientific questions it has already raised are far more interesting--to scientists, at least.
“I’d say it’s the most interesting question there is as far as cancer is concerned, but I suppose the most interesting field is always the one you’re in,” says Harry Gelboin, chief of the National Cancer Institute’s laboratory of molecular carcinogenesis.
The question is: can a product that has caused bladder cancer in rats also cause cancer in another part of the body in humans?
‘We Just Don’t Know’
The answer is: “We just don’t know. If we did, we would be a lot further along in understanding how cancer works and what to do about it,” Gelboin said.
The specificity of carcinogens to particular organs or tissues has long offered scientists tantalizing clues to the process of carcinogenesis itself. But while scientists have identified more than 500 carcinogens--from asbestos to dyes to urethane--the mechanism by which these elements turn cells cancerous still eludes them.
“We don’t know a lot about this, but we do know some things,” said Dr. John Lazlo, vice president for research at the American Cancer Society.
“For example,” he said, “we know that certain substances can get concentrated in the urine and sit in the bladder, where they can promote tumor growth. That is reputedly what happens with saccharin in rats, which is a very weak carcinogen otherwise.”
“But on the other hand, if you look at benzopyrene, one of the many carcinogens found in tobacco, it can cause cancer just about anywhere it can get to,” Lazlo said. “In smokers, you see it most often in the lungs because that’s the organ which bears the brunt of tar in cigarette smoke, but when it gets in the system it can also cause cancer of the pharynx, esophagus, pancreas and the bladder.
“And if you take that same carcinogen, in the form of chewing tobacco, and put it in the mouth, you get cancer of the cheek and of the gums and tongues.”
So then, on a very simple level, carcinogens are opportunistic.
“No, not really,” Gelboin said. “Anywhere where intimate contact with the carcinogen is present is obviously more at risk, but there are many carcinogens that only act on certain organs and certain tissues, even though they are present in others.”
The reason for this, Gelboin said, is that the carcinogens themselves do not promote tumor growth; something the carcinogens become once they enter the body do.
“Almost all carcinogens are considered toxins by the body,” he said. “But during the detoxification process, metabolites are formed which, in turn, may either be activators or promoters in the carcinogenic process.”
Some organs also may have particular chemical receptors which cause them to attract and metabolize certain carcinogens, making them more susceptible to the metabolites’ effects. Carcinogens can get amazingly precise in this way.
Straightforward Approach
“We have a chemical, dimethyl hydroxyzine, that pretty reliably induces colon cancer in experimental rats,” said Dr. Willard Visek, professor of clinical sciences at the University of Illinois Medical School in Urbana. “So, if we want to study colon cancer, we know a fairly straightforward way to get it.”
Several carcinogens are less straightforward, interacting with other carcinogens or other substances to create effects neither could separately. Asbestos--by itself implicated in mesothelioma, tumors of the internal body lining--may also enhance the carcinogenic effects of smoking, for example.
