Air pollution can cause lung cancer, but not because it causes genetic mutations, but because it causes an inflammatory reaction in the environment of cells that have acquired mutations for other reasons. With appropriate anti-inflammatory treatment, the appearance of cancer in tissues that have accumulated mutations can be prevented. This is demonstrated by international research led by the Francis Crick Institute in London, presented yesterday in the journal Nature.
The results represent a paradigm shift in the understanding of some cancers, as it relativizes the role of mutations and highlights that of inflammation. In addition, they open the way to improve the prevention of cancers caused by pollution and possibly other types of cancer. And they provide new arguments to limit air pollution.
Researchers have noted that areas with higher levels of fine particulate matter pollution, less than 2.5 microns, coincide with areas where there is a higher incidence of lung cancer in non-smokers. Three years of exposure to a high level of air pollution is enough for the risk of lung cancer to increase significantly.
Studies with mice and patient tissues have revealed that pollution-caused cancers do not have a genetic mutation profile that explains their origin, as do tobacco-caused cancers. The key is an inflammatory reaction in the lungs due to pollution. The reaction is characterized by the production of the interleukin-1 beta protein, against which there are already approved drugs. Mice treated with one of these drugs, the antibody canakinumab, developed fewer tumors.
"I had always thought that oncogenic mutations were necessary and sufficient for cancer. We need a new model" to explain how cancer starts, said Charles Swanton, director of the research, at a press conference on Tuesday.
First, genetic mutations accumulate in the cells, something that inevitably happens to all organs throughout life. An inflammatory reaction then takes place which, if it affects cells with oncogenic mutations, can initiate the disease.
This model explains a large proportion of lung cancer cases in non-smokers. Future studies will have to clarify which other types of cancer start in this way. Among the candidates, Swanton mentions mesothelioma, some head and neck tumors, and cancers related to obesity and alcohol, given that they are factors that cause inflammation.
Some of these tumors could be prevented in the future with a diet that limits the action of inflammatory molecules involved in cancer, says Swanton. Likewise, "if we understand these phenomena a little better, I hope that one day pharmacological prevention will be possible".
