A number of groups are presently working on ways to use viruses to precisely target and kill cancer cells. Here's an update on one of them from ScienceDaily: "The Senecavirus [is] harmless to normal human cells, but could infect certain solid tumors, such as small cell lung cancer, the most common form of lung cancer. ... Scientists at Neotropix say that, in laboratory and animal studies, the virus demonstrates cancer-killing specificity that is 10,000 times higher than that seen in traditional chemotherapeutics, with no overt toxicity. The company has developed the 'oncolytic' virus as an anti-cancer agent and is already conducting early phase clinical trials in patients with lung cancer. ... researchers went on to identify several areas on the viral protein coat that they think might hook onto receptors on cancer cells in the process of infecting them. ... It will be critically important to find out what region of its structure the virus is using to bind to tumor cells, and what those cancer cell receptors are. Then we can, hopefully, improve Senecavirus enough to become a potent agent that can be used with many different cancers."