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Evolution Has Spared Some Organs from Cancer

The reasons people and animals develop cancer in some organs but not in others may have more to do with evolution than genetic or lifestyle factors such as smoking, according to research published in Trends in Cancer. The paper argues that evolution has protected essential but unpaired organs, such as the heart, from tumour development while larger and often paired organs, such as the liver, are more likely to develop cancers as they might be less essential for survival.

Dr Beata Ujvari of Deakin University’s Centre for Integrative Ecology said the difference in cancer prevalence between organs had previously been accredited to intrinsic factors such as stem cell numbers and high mutation rates in certain organs, or to extrinsic factors such as cigarette smoking and pollution.

“We propose that also considering organs as distinct but connected eco­systems whose different vulnerabilities to malignant transformation may be partially explained by how essential each organ is for survival,” Ujvari said. “For example, the relative rarity of heart and brain cancers can potentially be attributed to the low cellular turnover in these organs, and therefore to the low opportunities for cancer-causing mutations.

“We think that turnover rates may also be low in these organs because they are crucial to survival. While the cell turnover rate is approximately 4–15% per year in the heart and 2.7% in the brain, the intestinal epithelium completely self-renews approximately every 5 days.”

The scientists predict that after the effects of stem cell numbers, rates of cell division and exposure to toxins and infection are taken into consideration, the ecology of different organs will account for considerable differences in vulnerability to cancer. They are currently working on a formal test to prove or disprove their hypothesis.

“This kind of evolutionary ecological analysis of variations in different organs may prove of great value in cancer prevention and treatment,” Ujvari said.