Why do cancerous cells use more glucose than regular cells?

Cancer is a disease at the cellular level. Tumours undergo rapid, unregulated cellular proliferation due to damage to their DNA. These cancer cells need to adapt their metabolism in order to survive and divide in the tumour environment (and its potentially metabolically compromised conditions). Cancer cells in these environments are left reliant on a constant supply of energy, and in characteristic metabolic changes to support survival and division, these cells have an increased uptake of glucose (alongside enhanced rates of glutaminolysis and fatty acid synthesis). [1]

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It is this increased uptake of glucose that is exploited in PET scanning. In being treated like glucose by the body, the radiotracer builds up in the cancerous cells, and it is these areas (the tumours) which are most radioactive, which is imaged by the scanners. 

 

After complete digestion of food (when the body is in the fasting state), most tissues have their energy supplied by free fatty acids. The brain always uses glucose, but many other cells only use glucose when its concentration in the body is high. After an intake of glucose (through eating), several tissues switch from free fatty acid to glucose metabolism. PET scanning is therefore often carried out in the fasting state, where glucose uptake by non-cancerous cells is low. This enables easier identification of the cancerous cells that are still using glucose. 

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Cancerous cells use glucose in preference to these free fatty acids, regardless of whether or not the glucose concentration in the body is low. If the cancerous cells are hypoxic (deprived of oxygen, usually due to the tumour environment), they use anaerobic metabolism, which requires much more glucose than aerobic metabolism, further extending the increased glucose metabolism by cancer cells. Whether or not they are hypoxic though, PET imaging takes advantage of the much-increased uptake of of glucose by the cancerous cells. [3]

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References:

[1] Fadaka, A. et al, (2017), Biology of glucose metabolization in cancer cells, Journal of Oncological Sciences, 3(2). pp. 45-51

[2] Cell Metabolism (Tochris). Available at: https://www.tocris.com/cell-biology/cell-metabolism. [Accessed 16/02/19]

[3] Jadvar, H., & Parker, J. (2005). Clinical PET and PET/CT. London: Springer. (pp. 49-53).