Fighting back

2019-03-07 04:12:01

By Nell Boyce in Washington DC A PROTEIN widely used to detect prostate cancer may not just be a harbinger of bad news. A new study shows that it actually fights cancer, and that drugs designed to block it might backfire. Doctors test men for prostate cancer by measuring blood levels of a protein called prostate-specific antigen (PSA). Men with prostate cancer have unusually high levels of PSA. High PSA levels are also found in some other cancers, suggesting the protein may encourage the uncontrolled cell division that occurs in tumours. Yet one study found that breast cancer patients with high PSA levels have a better prognosis. Intrigued by the contradiction, John Holaday and his colleagues at the pharmaceuticals company EntreMed in Rockville, Maryland, began to study PSA’s effect on cancer cells. They found that the protein didn’t alter the growth rate of prostate cancer cells or melanoma cells, but it did slow the growth of cells that make up blood vessels. Cancer researchers hope to starve tumours by blocking the blood vessels that feed them. So to find out if PSA can be beneficial, Holaday and his colleagues injected mice with melanoma cells and treated some of the animals with PSA. In those treated, there were 40 per cent fewer secondary tumours in the lungs than in untreated mice (Journal of the National Cancer Institute, vol 91, p 1635). Some researchers are developing anticancer drugs that actually inhibit PSA. “We would think that perhaps our findings might challenge that concept,