Cancers strike certain organs, such as the colon or breast, more often than others.
In an Opinion recently published in Trends in Cancer, researchers propose that this vulnerability in some organs may be due to natural selection.
Humans can tolerate tumors in large or paired organs more easily than in small, critical organs, such as the heart. Therefore, larger organs may have evolved fewer mechanisms to defend against cancerous cells.
Researchers suggest that the organs that are the most important to keeping us alive and capable of reproduction, such as the heart, brain, or uterus, may enjoy a better protection against cancer, all other things being equal.
Although this may be not the main factor to explain the different susceptibility of organs to cancer, it is a factor that contributes with others.
In the past, studies have explained the difference in rates of organ cancer by looking at either external risk factors, such as smoking or UV light exposure, or internal factors, such as how often cells must divide in an organ.
In the current paper, the team suggests that natural selection has favored strong anti-cancer protection for small organs that are critical to human survival and reproduction.
According to them, organs that are large or in pairs could potentially accumulate larger numbers of oncogenic manifestations without being impaired.
On the contrary, small and important organs like the pancreas could be easily compromised with only a few tumors inside.
Therefore, so the theory goes, the pancreas should be better at defending against cancer compared to an organ like the kidney, if all other factors are equal.
Anti-cancer protection mechanisms vary from organ to organ, but in general, they make an organ resistant to tumor formation.
The researchers also recommend that cancer biologists think of individual organs as specialized islands with their own environmental conditions (such as the level of oxygen, acidity, or water), where the survival of cancer cells depends on is the hospitality of the local environment.
It clearly means that certain organs are more favorable than others to malignant perturbation.
The researchers are now working to test their hypothesis. Currently, they are running a long-term experiment with mice to measure the accumulation of cancerous and precancerous mutations inside different organs.
The research is part of a new international collaboration between Deakin University in Australia and the French National Center for Scientific Research.
Citation: Thomas et al. (2016). Evolutionary Ecology of Organs: a Missing Link in Cancer Development? Trends in Cancer, published online. DOI: http://dx.doi.org/10.1016/j.trecan.2016.06.009.
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