HOW VACCINES CAN PREVENT CANCER
  
Vaccines against specific viruses could prevent one in ten cases of cancer in Britain – according to a new report by Cancer Research UK .
  
The report also estimates that a handful of infections can trigger around one quarter of cancer cases in the developing world and suggests that vaccines could stop them.
  
The authors of the report stress that people cannot “catch” cancer. But some viruses can initiate the disease in a small proportion of those infected.
  
Almost all kinds of cancer develop through a series of genetic accidents. When the accidents accumulate a cell can become cancerous. For some sorts of cancer one of these genetic accidents is linked to infection.
  
Cancers linked to infection with particular viruses include cancers of the cervix, liver and nasal passages (nasopharyngeal carcinoma) as well as certain types of lymphomas including some Hodgkin’s lymphomas and rare forms of leukaemia. Many cases of stomach cancer are also linked to a common bacterial infection.*
  
Although only a small proportion of virus-infected people develop these cancers, the global number of virus- associated cancer accounts for more than 1.8 million new cases of cancer each year  - which is around 18 per cent of all new cancer cases worldwide.
  
Professor Alan Rickinson, from the Cancer Research UK Institute at the University of Birmingham and lead author of the report, said: “Studying the association between infectious agents and human cancers is extremely important because, in such cases, infection represents one defined link in the chain of events leading to cancer development.
  
“Knowing this helps us to trace other links in the chain and to understand how the whole chain fits together. More importantly, if we can break the chain by preventing the infection through vaccination, then we can prevent the cancer developing.”
  
Development of a vaccine for cervical cancer – nearly half a million cases are diagnosed worldwide and almost 3,000 in the UK each year - is well advanced. Almost all cases of cervical cancer are caused by the human papilloma virus (HPV) and experts believe that the vaccine could prevent around 70 per cent of cervical cancer.
  
Dr Anne Szarewski, clinical consultant at Cancer Research UK , said:  “I do feel that the work we are doing on this vaccine is the most exciting development in cervical cancer research in many years. By using HPV vaccines we hope that, ultimately, we will be able to prevent the majority of cases. With any disease caused by a virus, the best way to stop it is to prevent it with a vaccine.
  
“But there are still a number of unanswered questions.  We don’t know yet how long immunity will last, and if booster vaccines will be required.  The longest period for which women have been followed up after an HPV vaccine trial has been four years.”  
  
A vaccine has also been developed for the Hepatitis B virus which is linked to liver cancer. There are 340,000 cases of primary liver cancer worldwide – half of which are linked to the Hepatitis B virus. There are 2,784 cases of this cancer in the UK each year but a much lower percentage of these are linked to the virus.
  
No vaccines have yet been developed to help combat stomach cancer, nasopharyngeal carcinoma and the lymphomas and leukaemias associated with infections.  
  
But Cancer Research UK is continuing to fund research into possible links between other cancers and underlying infection.
  
Professor John Toy, medical director of Cancer Research UK , said: “ It is very important that people understand they cannot catch cancer in the way they can catch a cold or flu virus.
  
“As today we successfully vaccinate against infectious diseases so we shall soon be able to vaccinate against certain types of cancer.”
  
(15/3/06)