\WASHINGTON (AP) -- Laboratory mice slathered with caffeine developed fewer skin tumors than untreated animals, suggesting the chemical that adds zip to coffee and tea also may protect against skin cancer, researchers say.
Dr. Allan Conney, a professor of cancer and leukemia research at Rutgers University, said a skin lotion spiked with caffeine or with another compound found in green tea reduced by more than half the number of skin tumors on hairless mice that had been exposed to high levels of ultraviolet radiation.
"We had between 50 to 70 percent tumor formation inhibition in the mice that were treated with caffeine or with EGCG (the other chemical compound)," said Conney, senior author of a study appearing this week in the online site of the Proceedings of the National Academy of Sciences.
Skin cancer is the most common cancer in the United States. The American Academy of Dermatology estimates about a million cases will be diagnosed in the country this year. Among them will be more than 88,000 new cases of melanoma, the disease's deadliest form. Skin cancer generally is curable by cutting, burning or freezing the tumor cells, but left untreated it can be deadly.
To test the effects of caffeine on skin cancer, Conney and his colleagues exposed 90 mice to high levels of ultraviolet radiation twice a day for 20 days. They used a strain of animals called hairless mice, commonly used for skin cancer studies.
After the mice got their UVB doses, the animals were divided into three groups. One group was anointed daily with a solution of acetone and caffeine. Another group received acetone and EGCG. The third group got skin applications of acetone only. Acetone is an organic solution often used on the skin.
At the end of 18 weeks, the three groups of mice were killed, and the level of skin tumor formation was analyzed.
Conney said mice in all three groups developed malignant skin tumors, called squamous cell carcinomas, but the number of tumors per mouse was reduced by 72 percent in those treated with caffeine and by 66 percent among those treated with EGCG, compared to the controls treated only with acetone.
The treated mice also had fewer nonmalignant, sunlight-related tumors, said Conney. Compared to the control group of mice, the mice treated with caffeine had 44 percent fewer nonmalignant tumors and the EGCG group 55 percent fewer, he said.
Conney said that although both compounds were effective in lowering tumor risk, caffeine has an advantage because it is chemically more stable than EGCG.
Unlike sun screen lotions, which protect against skin cancer by preventing the skin from absorbing ultraviolet rays from the sun, the caffeine's cancer protection works in the cells after exposure to the ultraviolet rays. Rays from the sun can cause genetic changes in the skin that can lead to skin cancer. Conney said caffeine apparently blocks this action by causing abnormal cells to kill themselves, a type of programmed cell suicide that prevents the development of abnormal growths.
"This is not a sunscreening effect," said Conney. "It is a biological effect."
He said the caffeine acts selectively, causing the abnormal cells to die but not affecting the normal cells.
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