An analysis of how cells in a tumour cooperate has provided a unique insight into the evolution of cancer, and may lead to new treatments.
It makes use of 鈥済ame theory鈥� 鈥� the mix of mathematics and economics theory that has been invaluable in understanding how cooperation can evolve in animal societies, even when individuals are selfish.
Robert Axelrod, a political scientist at the University of Michigan in Ann Arbor, US, a leader in applying game theory to evolutionary biology, has now turned his attention to cancer.
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Since every cancer cell within a tumour is different, with different mutations and needs, each of these cells can be thought of as a 鈥減layer鈥� in a game theory sense, Axelrod says.
Independently malignant
The 鈥済ame鈥� 鈥� to grow a successful tumour 鈥� proceeds more efficiently for all players if they cooperate, and this can occur without requiring the players to make conscious strategies.
鈥淚t鈥檚 well established that tumour cells grow by diffusing growth factors into the neighbouring tissue,鈥� says Axelrod. Some cells lack the 鈥渇ull deck鈥� of mutations necessary to produce all the growth factors, overcome host defences and become independently malignant.
But cells can aid each other by complementing the missing growth signals. A cell that promotes blood vessel growth to the tumour will also benefit other pre-cancerous cells.
鈥淚t鈥檚 Adam Smith鈥檚 old idea that if people cooperate it鈥檚 easier to get the job done,鈥� Axelrod says, referring to the 18th-century philosopher. 鈥淐ooperation is thought of as a good thing, and cancer bad. It may be the reason why no one has thought of putting the two together.鈥�
Diffusion chemicals
Recognising that tumour cells grow and recruit others through cooperation in this way has implications for understanding how cancer develops, and may lead to new approaches to therapy, Axelrod suggests.
鈥淔or example, you could change the micro-environment of a tumour so that the diffusion chemicals don鈥檛 travel so far,鈥� he says.
Laura-Jane Armstrong, at Cancer Research UK, says it is 鈥渧ery plausible鈥� that different subtypes of cancer cells may cooperate to support each other鈥檚 growth. 鈥淭his could also explain some of the differences seen within cells from the same tumour, and even how tumours can acquire resistance to treatments.鈥�
Axelrod and colleagues propose several methods to test the theory, and Armstrong says that if it is confirmed experimentally it could have major implications for how we treat cancer: 鈥淚f there are sub-populations of different cancer cells within a single tumour, it could mean multiple drugs are needed to target all the different types of cell that contribute to the cancer.鈥�
Journal reference: Proceedings of the National Academy of Sciences (vol 103, p 13474)
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