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Air pollution boosts cancer spread.

Air pollution boosts cancer spread

The brownish haze smothering Los Angeles and other smoggy cities not only makes breathing difficult but also encourages cancer spread within the body, animal studies suggest. The research also raises the concern that living in heavily polluted areas increases a cancer patient's chances of dying from the disease.

Arnis Richters at the University of Southern California School of Medicine in Los Angeles and his colleagues have evidence implicating nitrogen dioxide--a common pollutant from auto exhaust--in the lethal spread of cancer. For eight weeks they exposed mice to air containing 0.25 to 0.5 parts per million nitrogen dioxide (concentrations common in Los Angeles), then injected the mice with melanoma, a particularly serious type of skin cancer. After 21 days, the team reports, mice that had inhaled nitrogen-dioxide-laced air prior to the injections showed more tumors in their lungs than did control mice receiving the injections after inhaling pristine air. Furthermore, the mice exposed to nitrogen dioxide died sooner than the control mice.

"Our results indicate that inhalation of nitrogen dioxide facilitates the spread of blood-borne cancer cells," Richters says. Studies show that many people with cancer have millions of malignant cells circulating in their blood, especially during and immediately after surgery, when tiny tumor cells break off and enter the bloodstream, he says. In most cases, the immune system destroys these cells before they have a chance to take root in distant body parts. But Richters says his work suggests nitrogen dioxide in the air can impair certain components of the immune system, including the killer T-cells that attack tumor cells.

In addition, nitrogen dioxide appears to damage endothelial cells lining the lung capillaries, he says. Richters' work shows that platelets--clotting factors in the blood--plug the blistered walls of these cells, but the clogged areas ensnare migrating cancer cells that can go on to become lung tumors.

Whether the animal findings apply to people remains unclear, but Richters cites an Australian study showing that cigarette smokers with melanoma are more likely than non-smoking melanoma patients to experience early cancer spread. Cigarette smoke contains nitrogen dioxide, he notes.

The new evidence on smog hasn't prompted Los Angeles physicians to advise cancer patients to move away from the city, Richters admits. Still, he believes the implications may be strong enough to recommend that cancer patients breathe clean air during surgery and the risky postsurgical period.
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Author:Fackelmann, Kathy A.
Publication:Science News
Date:Apr 7, 1990
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