[LUM#6] Cancer, the disease of rupture

[LUM Magazine] - Published on July 18, 2017 in Science-Society

Cancer is rare in the animal kingdom. Species have always evolved to protect themselves from it. When this disease becomes widespread, it is because there has been a disruption in the natural environment. Extraordinary longevity, increased size, exposure to pollutants... Let's take a closer look.

Cancer, a recent disease? Let's dispel the myths. Far from being new, this worrying malignant tumor is as old as multicellular organisms themselves. It originates at the very heart of our cells. At the onset of cancer, a cell goes haywire, proliferating anarchically and becoming immortal. It reproduces, ignoring the warning signals from its neighbors, and can eventually form a malignant tumor or spread throughout the body. "Cancer is not something foreign to us. It is the manifestation of a malfunction in our own organism," explains Eric Assenat, head of the medical oncology department at Saint Eloi University Hospital.

The cause of this loss of control is a change in genetic information. "This can be due to a copying error or external factors such as smoking, radiation, viruses, bacteria, chemicals, etc.," explains the oncologist. When mutations accumulate within a single cell, it becomes cancerous.  

Each species has its own strategy

To combat this weakness, all multicellular living beings have developed protections over the course of their evolution. Elephants, for example, are very rarely affected. This is paradoxical, as these animals are 50 to 100 times heavier than humans: their large number of cells should lead to a significant number of mutations and therefore more cancers. "In reality, elephants have evolved to avoid certain cellular diseases, including cancer, with nineteen copies of the gene central to resistance to this disease in each of their cells. If one copy mutates, eighteen remain potentially active," explains Michael Hochberg, ecologist and researcher at the Institute of Evolutionary Sciences in Montpellier (ISEM).

Each species has its own defense strategy against disease. Most small animals die young, before genetic abnormalities accumulate in their cells. As for large animals, they live long lives, but have developed anti-cancer protection mechanisms over the course of their evolution. As a result, "in animals living in their natural habitat, the risk of developing cancer during their lifetime is around 1 or 2%, and to our knowledge does not exceed 5%," summarizes Michael Hochberg.

Breaks with the natural environment

So why is it that the incidence of this disease can sometimes skyrocket? "When the lifetime risk of developing cancer exceeds about 5%, it means that there is a disturbance in the ecology of the species. In animals, this happens in captive groups, in domestic animals, in animals with parasites, or in polluted environments , " explains Michael Hochberg (A framework for how environment contributes to cancer risk, in Ecology Letters, 2017).

Abnormal prolongation of life span, exposure to pollutants, reduction in genetic capital, infection by viruses... These are all disruptions to the natural environment that prevent the protective mechanisms put in place by evolution from coming into play. In zoos, the culprits are varied: contraceptives for cheetahs and tigers, cancer-causing viruses for prairie dogs, and artificially reduced genetic capital for Tasmanian devils.

In the wild, when cancer strikes several individuals, pollutants are obvious suspects. This is the case with white whales in Canada, contaminated by heavy metals and chemicals from the St. Lawrence River. "But it's not always easy to prove the link between cancer and the presence of pollutants,"Michael Hochberg cautions. Within the same species, the risk also increases with size. "In humans, being 10 cm taller increases the risk of cancer by about 5% in men and 8% in women ," explains the ecologist.

Longevity

But the key factor, the one that explains a large proportion of cancers, is ultimately longevity. This is because the risk increases with the number of genetic mutations in the cells and therefore with age. Laboratory mice have a 40% risk of cancer during their lifetime because, protected from predators, infections, and viruses, they live to be a year old or more, which is a remarkably long time!

Mechanically speaking, our current extraordinary longevity makes us vulnerable to this disease. Today, 40% of Americans develop cancer during their lifetime. In France, there are 400,000 new cases each year. 150,000 people die from it, with an average age between 60 and 70. "If cancer has become the leading cause of death, it is also because we are dying less from other causes ," says Eric Assenat.

So what can we do to combat this disease of disruption, given that we humans live in such a modified environment? We can, of course, refrain from smoking, drink less alcohol, reduce our exposure to UV rays and pollutants, eat a balanced diet, and engage in physical activity. And we can rejoice in the potentially revolutionary prospects for treatment.

Keywords: LUM#6, LUM Magazine, Research, Health, Company