Viruses may be behind up to 40 per cent of cancers including brain tumours and leukaemia, according to scientists.
If they are proved correct in further tests, it could pave the way for vaccinations against several types of cancer and therapies to cure them, the Daily Mail reported.
The claim is based on a study that has discovered viruses in types of cancer, which were never thought to be linked with infection.
It has been known for decades that viruses cause some types of cancer but it was thought to be only 10 to 20 per cent of cases.
The best known are the hepatitis B and C bugs, which can cause liver cancer, and the human papilloma virus (HPV) which can cause cervical cancer.
Now, scientists at the Karolinska Institute in Sweden have found a viral link with medulloblastoma, the most common form of childhood brain tumour.wo years ago it was discovered that Merkel cell carcinoma, an aggressive skin cancer, often follows infection by the polyomavirus that is common among animals and can spread to humans.
It is also claimed that viruses could cause prostate cancers.
Nobel Prize winner Harald zur Hausen, who jointly discovered the link between cervical cancer and HPV in the 1980s, said he expected more discoveries to follow and suggested that viruses could be involved in cancer of the skin, breast, gut and lungs.
"If we can understand how these viruses work we could prevent people from contracting them and even create therapies that use the patient's own immune system to destroy infected or cancerous cells," said Alan Rickinson, professor of cancer studies at Birmingham University.