A virus similar to that causing breast cancer in mice may play a role in causing breast cancer in women, suggesting that not only cancerogens are responsible for the disease. The study conducted by American researchers also shows that breast cancer could be spreading through populations.
They found traces of the virus, which is similar to one known to cause breast cancer in mice, in up to three-quarters of tumour samples taken from women worldwide.
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 colleagues from 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".