Results of the first clinical trial that looks at the impact of lycopene, which is found in tomato products, suggest it and other natural plant nutrients may be effective in preventing prostate cancer and treating the disease in its earliest stages.

Diets rich in tomato products, such as tomato sauce and ketchup, have long been associated with a reduced risk of various cancers, especially prostate cancer, but it has not been known why.

This study, published in the August issue of Cancer Epidemiology Biomarkers and Prevention, suggests the key cancer-fighting factor may be a combination of these plant nutrients, called phytonutrients, including lycopene, which is highly concentrated in tomato products. There is no data as yet to indicate these compounds are helpful in reversing or controlling later stage disease.

"There have been epidemiological studies but none that actually proves a cause-and-effect relationship between lycopene and reduced cancer risk.

Tomatoes contain a lot of other compounds that might explain the benefit," said Dr. Frederick Khachik, co-author on the study and professor of chemistry and biochemistry at the University of Maryland.

Researchers followed 30 men with localized prostate cancer, half of whom received 15 milligrams of lycopene daily while the other half received no intervention for three weeks prior to surgery.

Those who were treated had smaller tumors and tumors that were more likely to remain confined to the prostate, as well as lower levels of prostate specific antigen or PSA in serum, a common marker used to detect prostate cancer.

The treatment was a natural tomato extract, developed in Israel, called Lyc-O-Mato, which contains four times as much lycopene as actual tomatoes. But the extract includes other potentially helpful carotenoids, compounds from plants that absorb harmful free radicals in the body.

Khachik said the study involved very few patients but because it was the first study of its kind, reporting the data was important.

"We can't be 100 percent sure the benefit came from lycopene. More studies with larger numbers of people need to be done," he said.

Dr. Edward Giovannucci, professor of Medicine at Harvard Medical School, agreed.

"Because the numbers are so small, it is hard to conclude anything definitive from the study, but it is interesting," said Giovannucci, who has reviewed epidemiological studies on the purported cancer-fighting benefits of tomato products. It is a common misperception, he observed, to think that eating tomatoes is the best way to obtain those benefits.

"Tomato sauce, paste and ketchup produce higher levels of lycopene in the blood than tomatoes themselves," he said and added that perhaps the oil or cooking enhances the effect. Even some fast food diets contain a high amount of these healthful products.

Surprisingly, however, people who eat lots of fruits and vegetables do not necessarily have high lycopene levels. A few fruits, such as watermelon, have very low amounts of lycopene. The tomato, however, appears to be unique in its content of lycopene.

"Clearly, given the data that has emerged, if someone has few or no tomato products in their diet, he might want to consider taking lycopene supplements with other carotenoids," Khachik said.