Cancer is caused by anything that destroys cells, bacteria, viruses, chemicals, etc. when healthy cells are destroyed your body makes new ones using DNA and the more it has to do this the more the process fucks up with mutations because radiation particles flying through hit the dna molecules and knock some off, so your body forms tumors instead of healthy new cells. This is why we all die eventually of old age too. Cell replication breaks down. Scientists have to know this, they must just do "breakthrough studies" like this so they have something new to publish.