- Cancer of
critical organs like the heart, brain or the uterus occurs less often than
certain other types of cancer.
- Cancers of large
organs or organs that occur in pairs probably accumulate carcinogenic
- Critical organs
probably have evolved to have certain anti-cancer properties.
differences in the rate of occurrence of organ cancer have always been
attributed to external risk factors like smoking, exposure to UV light, the
diet consumed or even the rate at which the cells divide inside the body.
- Incidence of lung cancer has been attributed to smoking.
- Incidence of cervical cancer is attributed to the presence of sexually transmitted human papilloma virus.
- Incidence of colon cancer is attributed to polycyclic hydrocarbons and other carcinogens present in food.
in Organ Cancer Incidence
The discrepancies in the frequency of certain organs have been studied
previously with Jamie A Davies in the paper titled 'Inverse Correlation
Between an Organ's Cancer Rate and Its Evolutionary Antiquity' in the Journal Organogenesis
discussing the evolutionary aspect of organ cancer development.
The paper discusses that
certain organs developed later than other organ systems. This led to
evolutionary antiquity in certain organs with two possibilities attributed to
cancer rate discrepancies which include -
- The newly developed organs had less time
for selection pressure to remove neoplastic tendencies in the newer
- Another possibility that is discussed in
the paper is that newer organs have more complex genes that are more prone
to neoplastic changes, leading to the development of cancer.
The intrinsic property of the organ system
when coupled with extrinsic mutagens increase the risk for certain types of
cancer, according to the paper.
‘The heart may have developed better cancer-fighting mechanism than the breast.’
in Cancer Incidence
Frédéric Thomas, an
evolutionary biologist and his team from the Center for Ecological and
Evolutionary Cancer Research in France along with senior author Beata Ujvari
from Deakin University in Australia have propounded the belief that cancer
incidence could have an evolutionary angle to them, adding a fresh perspective
to the already existing beliefs.
According to the authors
whose opinion was published in the journal Trends in Science
that were bigger or which were paired had a greater tolerance for cancer than
smaller critical organs like the brain, heart or uterus. This means that larger
organs can tolerate cancers better than smaller critical organs and have
developed fewer defence mechanisms.
Thomas says "The
organs that are the most important to keeping you alive and capable of
reproduction, such as the heart, brain, or uterus, may enjoy a better
protection against cancer, all other things being equal. We are not saying that
this is the main factor to explain the different susceptibility of organs to
cancer, but it is a factor that contributes with others."
Evolution Has Favored
Natural Selection of Anti-cancer Properties of Certain Organs
According to the
authors, natural selection has given preference to anti-cancer properties in
small organs that are critical. This could be due to the fact that larger
organs can accumulate a lot more cancerous malformations while even a small
number of cancerous malformations in small organs could be critical.
"Organs that are large or in pairs could potentially accumulate larger
numbers of oncogenic manifestations without being impaired, whereas small and
important organs like the pancreas could be easily compromised with only a few
The team of researchers
are testing their hypothesis and are insistent that researchers should look at
individual organs as separate islands, with some organs being more conducive to
the growth of cancers than certain others.
The theory is based on
the premise that small critical organs will either
- Not tolerate the
growth of tumors and lead to annihilation of the being. There will not be
dissemination of the mutation in the form of offspring as the individual
or being cannot survive. Therefore, natural selection would ideally lower
the incidence of cancer in such critical and small cancers.
- Or have developed
anti-cancer properties that fend off potentially cancerous situations or
conditions. The development of such mechanism could, too, be dictated by
natural selection as these organs are critical.
Larger organs may be
able to 'accommodate' cancerous tumors for a longer period of time without the
tumor growth affecting their function, though their efficiency may be lowered.
This would provide the individual or organism time to procreate and to pass on
the mutant genes to the offspring.
The incidence of cancer
however, is not restricted to a single defining factor and is dependent on a number of factors. The researchers in the current study indicate that some organs may be better suited to cope with conditions like hypoxia (oxygen deficiency) and lack of nutrition as cancerous cells are also living cells and require medium for growth.
The Deakin University,
Australia and The French National Center for Scientific Research (CNRS) have
formed an International collaboration to study cancerous as well as
pre-cancerous lesions in the various organ systems in mice. The results of the
study will aid in throwing more light on the theory.
- Jamie A Davies "Inverse Correlation Between an Organ's Cancer Rate and Its Evolutionary Antiquity" Organogenesis, 2004.