Lycopene —the substance that gives tomatoes their red color — may be useful in fighting prostate cancer, according to new information published in the December 19 issue of the Journal of the National Cancer Institute (Vol. 93, No. 24: 1872-1879).

"For men with prostate cancer it would appear that there might be some slight advantage in consuming tomato products," said the study's chief author, Phyllis E. Bowen, PhD, RD, assistant professor of nutrition at the University of Illinois at Chicago (UIC).

But Bowen and another expert said there is not yet enough evidence to be sure about the benefit and safety of lycopene, and urged a careful approach.

Bowen and colleagues studied 32 men diagnosed with localized prostate cancer who ate about three-quarters of a cup of “off the shelf” tomato sauce on a pasta dish every day for three weeks before their prostatectomy (surgical removal of the prostate gland.

The tomato-sauce eaters were compared to another group of men with prostate cancer who also had their prostates removed, but didn't eat the tomato sauce.

Among men eating the sauce, blood levels of PSA dropped from 10.9 to 8.7, raising the possibility that the sauce was slowing the cancer's growth.

Tests after the prostate glands were removed showed increased lycopene levels in the blood and prostate glands of the tomato-sauce eaters, and less damage to their prostate cells' DNA — damage which can cause cells to turn cancerous—compared to the men who did not eat the tomato sauce. They also had less damage to the DNA of some kinds of immune system cells.

Bowen said although the researchers can't be certain, lycopene is likely a big reason those cells were protected, because it is a powerful antioxidant, which prevents damage to the cells.

Earlier studies showed men who ate more cooked tomatoes were less likely to get prostate cancer, and that lycopene slowed the growth of prostate cells grown in the laboratory.

Bowen said lycopene's apparent lowering of PSA levels is encouraging, because the substance is in any cooked tomato product, such as tomato paste, salsa, and ketchup.

But she noted it's too early to say for sure whether a dropping PSA means lycopene would actually slow the growth of prostate cancer in patients.

An ongoing clinical trial at UIC — still recruiting participants — will be better able to answer that question and others about lycopene's role in preventing or treating prostate cancer, Bowen noted.

"This was a well-designed and well-done study that provides more information about the biology of lycopene and how it may affect prostate cancer," said Durado Brooks, MD, director of prostate and colorectal cancer for the American Cancer Society.

"But the men in this study all had prostate cancer, so you can't say from this study what effect lycopene might have in preventing the disease in men with healthy prostates," Brooks added.

If lycopene lowered PSA without slowing the cancer, it could make treatment decisions much tougher for doctors, Brooks noted.

And a similar substance in carrots — beta-carotene — was once considered possibly useful to lower risk of lung cancer, but turned out to increase risk in some people, he observed.

Brooks says the advantage of gaining new information from clinical trials, such as the ongoing one at UIC, is safety. Such studies are under close medical supervision.

"In the meantime, we know for sure that eating at least five servings of fruits and vegetables every day lowers the risk of many cancers, and is safe. So that is one of the most important things you can do to help prevent cancer," concludes Brooks.