A new disease is affecting developing countries, deadlier than malaria, AIDS and tuberculosis combined. With changes in lifestyles, cancer is spreading in southern countries. Today, more than 70 % of the 7.5 million deaths in the world occur in countries with low or middle income. Faced with this alarming fact, IRD scientists and their partners are trying to specify the decisive factors in the illness. They are studying how natural selection has enabled animals to be more or less resistant to the development of certain malignant cells.
Understanding the disease at source
Cancer is the abnormal and disordered production in the body of cells, known as "malignant." During evolution, living beings have put in place natural mechanisms to control this unwanted proliferation and prevent too frequent development of these tumours. Scientists at the Centre for ecological and evolutionary research (Creec) in Montpellier, are studying how natural selection has designed this resistance to cancer in various species.
A yet unexplained paradox
To understand how the body's defences are used, scientists have examined a paradox, known as "Peto's paradox," named after the biologist who discovered it in the 1970's. The larger an animal, the more cells it has and the greater the risk of contracting a cancer. Yet, this is not the case in nature. Using a mathematical model, the research team explains this contradiction in a recent study.
The whale and the mouse: each has its priorities
The scientists showed that the larger the species, the lower the probability of activating genes involved in oncogenesis and the higher the probability of activating tumour-suppressant genes. Species such as beluga, weighing up to 2 tonnes, have lasted throughout evolution by deploying these cancer-fighting mechanisms. However, for a 2-gram mouse, the risk of contracting the disease is low before being devoured. From this viewpoint, it is of no advantage to develop this type of resistance. It seems more judicious in its case, to select other functions (predator avoidance, early sexual maturity, etc.), to ensure numerous progeny.
This new angle of approach to cancer research, by studying selective processes, will define which species are more resistant to the disease and better explain its decisive factors. Ultimately, this work could improve disease prevention.
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