Why don’t elephants have cancer?

For almost a year I got hooked by Naked Genetics podcast brought by The Naked Scientists in association with the Genetics Society. A few words to be said about  Dr. Kat Arney, curator of the podcast. Dr.Kat Arney has PhD in biology from Cambridge University and currently working on a popular science book about genetics. At the same time she is a media spokesperson, professional speaker, talented musician, and in fact a perfect example of multipotentialite.

Dr. Kat Arney’s Naked Genetics podcast is a great learning for both genetic scientists and people with zero knowledge in biology. Each episode usually covers latest news in rapidly growing world of genetics, provides interview with expert, and showcases gene of the month. It is very well structured content where hard science is explained in simple language which everyone can understand.

Today I discovered why elephants and whales don’t have cancer.

Every living thing on this planet is made of cells. Each living cell carries a DNA molecule, which stores genetic information. That information is being accurately copied and transmitted to the next generation of cells to ensure that the life continues.

Athena Aktipis from the University of California conducts a research on the evolution of cancer. She admits that cancer constitutes a fundamental problem for the evolution of multicellular organisms. In order to function properly multicellular body needs all cells work in cooperation. Cancer causes a breakdown of that cooperation. As a result DNA repair mechanisms get deactivated and the body eventually wanes.

If every cell has some chance of becoming cancerous, large, long-lived organisms should have an increased risk of developing cancer compared with small, short-lived organisms. The lack of correlation between body size and cancer risk is known as Peto’s paradox.

Where does cancer come from for any given individual? According to Aktipis, cancer is a result of evolutionary process within the body: cancer cells increase in a frequency and population. What happens is that within the body selection favours cells that are are not behaving properly in the body unless the immune system is able to keep them under control.

But from the evolution of life prospective, formation of multicellularity requires suppressing cancer. This is where we start thinking that higher species might have higher risk of cancer, simply because they have more cells in their bodies. However that is not the case. In fact, elephants and whales have lower rate of cancer.

Aktipis presumes that risk of cancer has a direct link to overall lifestyle of a particular animal. For instance a lifespan of field mice is about 1-2 years. They are “live fast, die young” type of animals. Hence it doesn’t make sense for field mice to invest more of the body resources in cancer protection mechanisms.

On the other hand larger organisms like elephants have to grow bigger and reproduce later, so their bodies put more resources on cancer protection. Yet that is only one part of the story.

Dr. Josh Shiffman with his team from the University of Utah conducted a research on elephants vs.human blood. Blood cells of an elephant and a human were bombarded with radiation. In this experiment the researchers were able to examine how the blood cells respond to DNA damage caused by radiation. What they found was that the cells in elephant’s blood didn’t stop its dividing or repairing DNA damage any faster than human cells, but it had an increased cell death. “It’s as if the elephants said, ‘It’s so important that we don’t get cancer, we’re going to kill this cell and start over fresh,” says Schiffman. “If you kill the damaged cell, it’s gone, and it can’t turn into cancer. This may be more effective of an approach to cancer prevention than trying to stop a mutated cell from dividing and not being able to completely repair itself.”

Finally here’re three key takeaways from Prof.Mel Greaves from The Institute of Cancer on how to deal with cancer:

  • prevention
  • early diagnosis
  • multi-combinatorial treatment

and this is extremely useful thing to know!

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