A universal law that describes the growth of animals also seems to describe the growth of tumours. Though the work is only in its early stages, researchers are already using it to explore the way cancers invade healthy tissue.
As an animal鈥檚 mass increases, so does the number of cells within it. But the blood supply that feeds those cells grows more slowly. As a result, an increasing proportion of the available nutrients go towards maintaining existing cells rather than the growth of new ones, so the rate of growth slows and ultimately comes to a halt.
In 2001, a team at Los Alamos National Laboratory in New Mexico showed that when differences in size and lifespan are eliminated, all the species they examined followed the same growth curve (Nature, vol 413, p 628). Since tumours also depend on blood supply for their nutrients, can similar equations be applied to tumour growth?
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Thomas Deisboeck of the Harvard-MIT Martinos Center for Biomedical Imaging in Cambridge, Massachusetts, and a team at the University of Turin, Italy, decided to find out. When they compared their predictions to the growth of 13 rodent or human tumours, they found the tumours鈥� growth closely followed the same universal law.
鈥淲e are convinced this work provides important new insights into the biology of tumours,鈥� says Deisboeck.
Genetically uniform
鈥淭hese are sophisticated and really clever studies,鈥� says Reinhard Ebner of Avalon Pharmaceuticals in Maryland. 鈥淏ut they represent idealised situations.鈥�
Ebner points out that the tumours Deisboeck examined were genetically uniform. But in many patients, tumours contain cells with different genetic mutations. Tumours can also alter their environment, creating new blood supplies to accelerate their growth.
Deisboeck agrees that the law in its present form does not offer a complete description of all tumour behaviour, and he and his colleagues are working on more sophisticated models.
He argues that studying exceptions to the law could reveal other interesting aspects of cancer biology. 鈥淒iscrepancies suggest that tumours may use certain tools or weaponry to overcome obstacles in their environment such as nutrient deficiency or mechanical stress,鈥� he says.
One of these weapons, his current work suggests, may be to invade other tissues. Eventually, he hopes an advanced form of his model might help clinicians to figure out suitable doses of anti-cancer drugs.
Journal reference: Journal of Theoretical Biology (vol 225, p 147)