Essential organs tasked with keeping us alive and reproducing – such as the heart, brain or uterus – may have evolved better protection against cancer than larger and paired organs, we have proposed.
In an article published today in the journal Trends in Cancer, we hypothesise humans can more easily tolerate tumours in large or paired organs than in small, critical organs. Therefore the larger organs may have evolved fewer cancer defence mechanisms.
Malignant tumours are more commonly found in larger, paired organs that are potentially less essential to survival and reproduction. Previous studies have attributed such organ-specific cancer difference to either external factors, such as smoking, or internal factors, such as the frequency of cell division in the organ.
We propose that natural selection theory could supplement these understandings. We also hypothesise that small, important organs could easily be compromised even when they carry only a few tumours, while larger organs can carry the burden of malignant transformations.
We are not saying this is the explanation for the different susceptibility of organs to cancer, but believe it could be a contributing factor.
An evolutionary approach to cancer research can offer new perspectives to therapeutic solutions.
Elephants and humans
Despite significant discoveries and treatment advances, human interventions can claim only a 5% reduction in cancer deaths since the 1950s. And this result is almost entirely attributable to increased awareness of risk factors and early detection.
Reporterruthie/Flickr, CC BY
A key contributor to the failure to find a magic bullet to cure cancer is that its progression is an evolutionary process. Cancer appeared more than half a billion years ago and has been observed in nearly the entire animal kingdom, from bivalves to whales.
Its appearance has been linked to the evolutionary transition from unicellularity to multicellularity. The latter requires a high level of co-operation among cells and the suppression of uncontrolled reproduction, known as proliferation, of individual cells.
With organisms increasingly being made of more complex cells, having a longer lifespan and larger bodies comes the likelihood of proliferation that can lead to malignant tumours.