Common viruses may play a bigger role in cancer than anyone thought.

It is well known that certain viruses can trigger specific cancers. Human papillomavirus, for example, causes around 93 per cent of cancers of the cervix. Now Dominik Duelli and Yuri Lazebnik at Cold Spring Harbor Laboratory in New York and colleagues have found evidence for how they might do it.

During tumour development, the chromosomes of affected cells often become wildly rearranged, but no one knew why. Duelli and Lazebnik suspected that cell fusion – when two or more cells unite by merging membranes – might be to blame. Several common viruses can initiate this process.

To test their idea, the researchers took human fibroblast cells with genes that made them more likely to turn into a tumour and infected them with a retrovirus that can cause fusion. Sure enough, fused cells had many more chromosomal abnormalities than unfused ones, and when transplanted into mice, only the fused cells produced tumours (Current Biology, DOI: 10.1016/j.cub.2007.01.049).

The team is now asking other cancer researchers to examine tumour samples for signs of cell fusion.