Table 2.

Mechanisms by which tumor cells resist radiation and chemotherapeutic drugs.

Radioresistance	Chemoresistance
Tumor hypoxic condition	Increased drug efflux and decreased drug uptake
Increased cellular production of cellular antioxidants	Inactivation of apoptosis
Activation of certain proto-oncogenes, and stromal interactions	Increased drug metabolism and drug compartmentalization
Amplification of DNA repair genes	Increase in the repair of DNA damage
Cancer stem cells as contributors to radioresistance	Increased or altered the drug targets
Survival signals favoured by transcription factors	Survival signals favoured by transcription factors