WASHINGTON — A new test demonstrating the link between smoking and genetic damage raises hopes for finding the components of cigarette smoke that cause cancer, scientists said Thursday.
Their research involves radioactive testing of the placentas discharged after birth from women who smoked during pregnancy.
In the short term, the results appear to affirm the longstanding assumption that smoking is potentially hazardous to babies as well as their mothers.
But the research has broader implications concerning the search for specific chemicals in cigarette smoke that could trigger the onset of cancer by damaging DNA, the body's basic genetic material, said Kurt and Erika Randerath of the Baylor College of Medicine in Houston.
It should eventually be possible to identify such a cancer-inducing chemical or chemicals, "maybe in a year, maybe three to five years," Randerath said.
And that would raise the possibility of blocking or removing such chemicals, "but that's far-fetched for now," he said in a telephone interview.
Mrs. Randerath said that, although the key link between smoking and genetic damage has only been suspected, the new test provides "a direct demonstration" of such a tie.
Onset of Cancer
That is important because the onset of cancer is believed to involve damage to DNA, as shown by the fact that many known cancer-causing chemicals produce certain changes--chemical addition products, or adducts--in experimental animals.
The new report, published in today's edition of the journal Science, was submitted by researchers from the National Institute of Environmental Health Sciences, Columbia University's College of Physicians and Surgeons and the University of North Carolina Medical School in addition to those from Baylor.
The new test shows "for the first time that cigarette smoke is associated with . . . a specific chemical fault in DNA of smokers that is absent in the DNA of nonsmokers," Randerath said.
The trick now is to match the damage-revealing adduct they found in nearly all the tested women smokers to some chemical or mixture of chemicals in cigarette smoke.
The scientists have failed in early tests to find such a match. But they said that could merely mean the particular adduct they have found is formed only in human or placental tissue or that it results from a smoke component not yet tested.
In the meantime, they said, finding a smoking-related adduct consistently showing DNA damage gives a crucial starting point for further research.
The report said cigarette smoking has been well established as "the major single known cause" of cancer deaths in the United States. And it added that tobacco smoke contains many substances that animal tests have shown cause cancer.
"But it is not clear which of the several thousand components of this complex mixture are responsible for human carcinogenesis," the report said.
As for the pregnant women and their offspring, the report said that a separate recent study indicated a relationship between DNA adducts in the placentas of animals exposed to various cancer-causing chemicals and adducts in many other organs in those animals.