Despite dramatic advances in our understanding of the disease, the evolutionary origin of cancer remains a mystery. Earlier claims that cancer is an entirely man-made disease fuelled by modern lifestyles have been discredited, especially given the recent discovery of tumors in a 3,000-year-old skeleton. But when did this disease start to appear in organisms? A new study, published in Nature Communications, presents evidence to suggest that cancer could be as old as multi-cellular life on Earth.
The majority of cancers are caused by faulty genes. More specifically, mutations in two classes of genes, known as proto-oncogenes and tumor suppressor genes, lead to tumor development. While the list of genes associated with cancer is extensive, the origin of these genes was unknown.
In order to shed light on the evolution of this disease, a team of scientists scoured databases of genes for hints of the origin of genes associated with cancer. “Our data predicted that the first multi-cellular animals already had most of the genes which can cause cancer in humans,” co-author Tomislav Domazet-Lošo said in a news-release. However, the researchers lacked evidence to demonstrate that these primitive animals experienced tumors, until now.
After years of study on the regulation of tissue growth in a group of simple animals similar to corals, called Hydra, the scientists finally unearthed hints about the roots of cancer by discovering naturally occurring tumors in two different species of this organism. This demonstrates that primitive and evolutionary ancient animals do indeed experience tumors. The team also discovered that the tumors negatively affected the organisms since they resulted in a significant reduction in fitness.
Furthermore, they were also able to infer the molecular mechanisms that caused the tumors to develop. They suggest that they are likely the result of female gametes (reproductive cells) failing to differentiate and accumulating in large numbers which were not removed by programmed cell death. Another interesting finding was that the tumors were only found in female Hydra and they bore a resemblance to human ovarian cancers.
Further molecular analysis of the organisms revealed a particular gene was dramatically over-expressed in the tumor cells which is normally involved in programmed cell death. “As a non-functioning cell death mechanism is also made responsible for the growth and spread of tumors in many types of human cancer, striking similarities appear here to cancer in humans,” said co-lead author Alexander Klimovich of Kiel University.
The researchers were also able to demonstrate that the tumor cells were invasive since transplant of the tumors into a healthy organism resulted in the development of cancer. According to lead researcher Thomas Bosch, this suggests that the invasive nature of cancer cells is also an evolutionary old characteristic.
In sum, this study has demonstrated that tumors have deep evolutionary roots. The researchers believe that studies such as this may further our knowledge of the fundamental mechanisms of tumorigenesis which could one day help us in the ongoing battle against cancer.