Common viruses that cause measles and skin infections may also raise the risk of lung cancer, scientists warn today.
Tests on cancer patients revealed that many had tumours that were infected with measles or the human papilloma virus, which typically causes warts but in some cases can lead to life-threatening cervical cancer.
The research, by two teams working independently in the US and Israel, suggests that viruses play a greater role in cancer than previously thought.
The scientists behind the studies believe the viruses may make healthy cells more vulnerable to dangerous mutations, and so exacerbate the effects of smoking and other well-known causes of cancer.
Lung cancer is the most common cancer in the world, with 1.3 million new cases diagnosed each year. More than 90% of these are caused by cigarette smoking. Lung cancer has one of the lowest survival rates of all cancers, with one person in Britain dying of the disease every 15 minutes.
Arash Rezazadeh, a cancer specialist at the University of Louisville in Kentucky, tested 23 patients with non-small cell lung cancer, which accounts for more than 85% of all lung cancers. Six patients had tumours that were infected with human papilloma virus (HPV), though one was later found to be a cervical cancer that had spread to the lungs.
The five remaining patients tested positive for different strains of HPV, with two patients infected with a type called HPV-16, which is responsible for half of all cervical cancers.
"The fact that five out of 22 non-small cell lung cancer samples were HPV positive supports the assumption that HPV contributes to the development of [the disease]," Dr Rezazadeh said. The work is to be announced at the European Lung Cancer conference in Geneva today.
Signs of infection
A second team of scientists at the conference, led by Samuel Ariad at Soroka Medical Centre in Beer Sheva, Israel, analysed tumour tissue from 65 patients with non-small cell lung cancer and found 54% showed signs of infection by the measles virus. "Measles virus is a ubiquitous human virus that may be involved in the pathogenesis of lung cancer," said Prof Ariad. "Most likely, it acts in modifying the effect of other carcinogens and not as a causative factor by itself."
Ed Yong at Cancer Research UK said: "We know that infections are involved in the development of some cancers such as cervical cancer. It's not impossible that they are also involved in the development of lung cancer in smokers, but we can't say for sure based on these preliminary studies. Neither study examined how common the viruses are in lung tissue from healthy people. The vast majority of lung cancers are caused by smoking, so avoiding tobacco remains the best way to prevent this type of cancer."
Professor Hans Stauss, an expert on cancer and the immune system at the Royal Free Hospital in London said it was too early to say whether vaccines against HPV and measles might reduce a person's risk of developing lung cancer. "There are certainly cancers that are caused by viruses and for those there are already effective vaccines, but at the same time, we are continuing to look at whether there are additional viruses that might cause cancer, in which case they could also effectively be treated with a vaccine."