Cancer cells derive energy from -
Cancer cells are dependent on aerobic glycolysis for continued growth.
Fast growing, poorly-differentiated cancer cells characteristically show high aerobic glycolysis.
A Serine/threonine kinase Akt stimulate glycolysis in malignant cells.
Activation of Akt oncogene is sufficient to stimulate the switch to aerobic glycolysis characteristic of cancer cells and Akt activity renders cancer cells dependent on aerobic glycolysis for continued growth and survival.

Following information have been added in 8th /e of Robbins 

Even in the presence of ample oxygen, cancer cells shift their glucose metabolism away from the oxygen hungry, but efficient, mitochondria to glycolysis.
This phenomenon called the Warburg effect and also known as aerobic glycolysis.
This metabolic alteration is so common to tumors that some would call it the eighth hallmark of cancer:
Clinically, the "glucose-hunger" of tumors is used to visualize tumors via positron emission tomography (PET) scanning, in which patients are injected with 18F-Fluorodeoxyglucose, a non-metabolizing derivative of glucose that is preferentially taken up into tumor cells (as well as normal actively dividing tissues such as bone marrow).
Glycolysis
Oxidative metabolism
Increased mitochondria
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