[LUM#6] Cancer: A Disease of Disruption

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

In the animal kingdom, cancer is rare. Species have always evolved to protect themselves against it. When this disease becomes widespread, it is a sign that a disruption has occurred in the natural environment. Extraordinary longevity, increased size, exposure to pollutants… An in-depth look.

Is cancer a recent phenomenon? Let’s dispel some myths. Far from being a new phenomenon, this alarming malignant tumor is as old as multicellular organisms themselves. It originates at the very core of our cells. At the onset of cancer, there is a cell that goes haywire, proliferating uncontrollably and becoming immortal. It reproduces, ignoring the warning signals from its neighbors, and may eventually form a malignant tumor or spread throughout the body . “Cancer is not something foreign to us. It represents a malfunction of our own body, ” explains Eric Assenat, head of the medical oncology department at Saint Eloi University Hospital.

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

Every species has its own strategy

To counter this vulnerability, all multicellular organisms have developed defenses over the course of their evolution. Elephants, for example, are very rarely affected by it. A paradox. These animals are 50 to 100 times heavier than humans: their large number of cells should lead to a significant number of mutations and, consequently, more cancers.“In reality, elephants have evolved to avoid certain cellular diseases, including cancer, by having nineteen copies of the key gene for resistance to this disease in each of their cells. If one copy mutates, eighteen potentially active copies remain ,” explains Michael Hochberg, an 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 can accumulate in their cells. As for large animals, they live long lives, but over the course of their evolution have developed mechanisms to protect against cancer. As a result,“among animals living in their natural habitats, the risk of developing cancer during their lifetime is around 1 or 2 percent, and to our knowledge does not exceed 5 percent,” summarizes Michael Hochberg.

Disconnections from the natural environment

How is it, then, that the incidence of this disease can sometimes skyrocket? “When the lifetime risk of developing cancer exceeds about 5%, it means there is a disruption in the species’ ecology. In animals, this occurs in captive populations, among domesticated 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 increases in lifespan, exposure to pollutants, reduced genetic diversity, viral infections… All of these represent disruptions to the natural environment, preventing the protective mechanisms developed through evolution from taking effect. In zoos, the culprits are varied: contraceptives for cheetahs and tigers, cancer-causing viruses for prairie dogs, or an artificially reduced gene pool for Tasmanian devils.

In the wild, when cancer strikes multiple individuals, pollutants are obvious suspects. This is the case with beluga whales in Canada, which are contaminated by heavy metals and chemicals in the St. Lawrence River.“But it’s not always easy to prove the link between cancer and the presence of the pollutant,”Michael Hochberg notes. 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 accounts for a large proportion of cancers—is ultimately longevity. This is because the risk increases with the number of genetic mutations within cells and, consequently, with age. Laboratory mice have a 40% lifetime risk of cancer because, protected from predators, infections, and viruses, they live to be a year old or even older—a remarkable age!

Simply put, today’s extraordinary human lifespan makes us vulnerable to this disease. Today, 40% of Americans will 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 fewer people are dying from other causes ,” explains Eric Assenat.

So what can we do to combat this degenerative disease, given that we humans live in such a heavily altered environment? We can, of course, avoid smoking, drink less alcohol, limit our exposure to UV rays and pollutants, eat a balanced diet, and stay physically active. And we can look forward to potentially revolutionary developments in treatment.

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