Scientists at London's Imperial College are testing the safety of a virus that has been engineered to shrink deadly brain and breast tumors. The treatment is based on a phage; a kind of virus that normally only attacks bacteria.

When tested in dogs, the phage shrank tumors and, in some cases, made them completely disappear. It will be tested in its first ever human trial later this year. 

Razor's Emma Keeling went along to meet the Professor leading the project, to find out what a phage actually is.