In some cases, the fusion of human cells is a normal process that leads, for instance, to the formation of muscle and bone. Viral infections can also cause cell fusion, but cells fused by viruses are widely considered to be harmless because they are generally believed to die without consequences for the host.
According to a recent study, however, cell fusion triggered by viruses is a possible contributing factor in the development of human cancer. The study also raises concerns about the use fusogenic viruses as vectors for human gene therapy or in other clinical applications owing to the possibility that such viruses might cause cancer.
The idea that aberrations in the number or structure of chromosomes can spur tumor formation is more than a century old. Such aberrations--known collectively as "aneuploidy"--arise in two principal ways: as a consequence of abnormal cell division, or as a result of cell fusion. By either mechanism, the resulting aneuploid cells no longer have the proper genetic makeup and frequently die. But researchers now know that tumor cells are often aneuploid--and very much alive. Whether aneuploidy is a cause or a consequence of a cancerous cellular state is the crux of a current debate.