Genistein, a compound found in soybeans, dramatically slowed the spread of prostate cancer in animal tests, reports the Journal of the American Association for Cancer Research. The researchers behind the discovery, from Northwestern University, say that the amount of genistein used in the experiments was no higher than what a human would normally eat in a soybean-rich diet.
The experiments established that genistein decreased metastasis of prostate cancer to the lungs by 96 percent compared with mice that did not eat the compound in their food - making the study the first to demonstrate genistein can stop prostate cancer metastasis in a living organism. "These impressive results give us hope that genistein might show some effect in preventing the spread of prostate cancer in patients," said Raymond C. Bergan, the study's director.
Bergan and his team have previously demonstrated in prostate cancer cell cultures that genistein inhibits detachment of cancer cells from a primary prostate tumor and represses cell invasion. In this study, the investigators fed genistein to several groups of mice before implanting them with an aggressive form of prostate cancer. The amount of genistein in the blood of the animals was comparable to human blood concentrations after consumption of soy foods, the researchers noted.
They found that while genistein didn't reduce the size of tumors that developed within the prostate, it stopped lung metastasis almost completely. They repeated the experiment and found the same result. Paradoxially, the study also found that mice fed genistein expressed higher levels of genes that are involved in cancer cell migration. "What we think is happening here is that the cells we put in the mice normally like to move. When genistein restricted their ability to do so, they tried to compensate by producing more protein involved in migration. But genistein prevented those proteins from being activated," Bergan explained. "This is really a lesson for researchers who depend on biomarker studies to test whether a treatment is working. They need to be aware that those biomarkers might be telling only half of the story."
Other human observational studies have found that while the spread of prostate cancer is reduced in men who eat soy-rich foods, findings have been mixed as to whether prostate cancer incidence is markedly different. Results of some laboratory studies of genistein have also been mixed, but most have shown favorable results.
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Source: American Association for Cancer Research