Vaccines against a wide range of viruses could one day prevent one in 10 cancers in the UK, suggests a new report. And the impact could be even greater in the developing world, where an estimated one in four cases of cancer is linked to infections.
Such vaccines could prevent hundreds of thousands of cases of cancer each year, according to the non-profit organisation Cancer Research UK. Its report, released on Monday, notes that roughly 18%, or 1.8 million cases, of all new cancers worldwide each year are linked to infections, although no vaccine exists against many of the related viruses.
But experts stress that you cannot “catch” cancer, and the viruses linked to the disease are not easily transmissible. “If you chat to your neighbour with cancer you’re not going to catch it. The cancer itself is not infectious,” says Rob Newton, an epidemiologist for Cancer Research UK. “You don’t vaccinate against cancer – you vaccinate against the infectious agents that cause it,” he explains.
Viruses can disrupt a cell’s inner machinery, including its DNA, leading to the uncontrolled cellular replication that gives rise to tumours.
Newton says that many liver cancers could be prevented with the already available vaccine against hepatitis B. This virus, which causes inflammation of the liver, is especially prevalent in southeast Asia and sub-Saharan Africa, where there is a great need for vaccine distribution.
People with chronic hepatitis B have a 20- to 100-times’ higher risk of liver cancer than uninfected individuals. And about 50% of liver cancers worldwide test positive for the hepatitis B virus.
Epidemiologists also say that almost all cases of cervical cancer test positive for human papilloma virus (HPV), which infects cells of the skin or inner mucosal surfaces, and is sexually transmitted. Newton says that studies of US university students found that about 50% of individuals are carriers of HPV. However, only certain strains put women at higher risk of cervical cancer.
In 2005, scientists announced that a vaccine against HPV proved successful in a trial involving more than 10,000 women. But it may take many years before further testing is complete and the vaccine becomes widely available.
There is work underway to find effective vaccines against other cancer-related infectious agents, including the Epstein-Barr virus that appears in some rare cases to promote tumour growth after many years of infection.
Researchers are also looking for new ways to fight against Heliobacter pylori, a common stomach bacterium. About half of the world’s population is infected with H. pylori, with many of these cases appearing in poor countries.
According to the new report, people who have endured a long-term H. pylori infection have a four- to sixfold increased risk of subsequently developing gastric adenocarcinoma, the most common form of stomach cancer worldwide.
Journal reference: CancerStats: Infectious Agents and Cancer (Cancer Research UK, March 2006)