Breast cancer 'may be caused by virus'

Breast cancer may be caused by a virus, American researchers claimed yesterday. Traces of the virus, which is similar to one known to cause breast cancer in mice, have been found in up to three-quarters of tumour samples taken from women around the world.

Breast cancer may be caused by a virus, American researchers claimed yesterday. Traces of the virus, which is similar to one known to cause breast cancer in mice, have been found in up to three-quarters of tumour samples taken from women around the world.

Nine out of 10 of the samples that contained the virus were from aggressive breast cancers, suggesting it may cause a more virulent form of the disease.

Paul Levine and his colleagues at the George Washington University School of Public Health, say in the online edition of the journal Cancer: "These findings provide increasing evidence for a human breast cancer virus with geographic differences in prevalence."

But the findings were dismissed by a British expert. Rob Newton of the Cancer Research UK epidemiology unit at Oxford, said the virus that causes breast cancer in mice had been identified in 1936, and researchers had spent decades looking for a human equivalent but had failed to find it.

"The evidence [for a human equivalent] remains deeply unconvincing and deeply contentious," he said.