(March 12, 2015) Parvoviruses can destroy cancer cells and are currently being tested in a preliminary clinical trial to treat malignant brain cancer. For their replication, the viruses need a particular enzyme in the cell. Scientists from the German Cancer Research Center (DKFZ) have now discovered that in healthy human cells, parvoviruses are unable to activate this enzyme. In many cases of malignant brain cancer, however, the enzyme is permanently active. As a result, this enables the viruses to replicate and to destroy the cancer cells. It accounts not only for the viruses' natural selectivity for cancer cells but also helps identify cancer patients who might benefit from parvovirus therapy.