<b>Testing for predictive markers is usually done on the paraffin block tumor.</b>

Information obtained from predictive markers give an indication of how effective clinically indicated chemotherapy agents might be in treating the patient's tumor cells. This is different from sensitivity/resistance testing.

<b>MDR-1 (P170 Glycoprotein) Multidrug Resistance</b>
For example, MDR-1 (P170 Glycoprotein) acts as an efflux pump to rid the cell of toxins and alien metabolic products. Expression of increased levels of MDR-1 by tumor cells is associated with resistance to natural product chemotherapy agents such as Taxol, Doxorubicin, and Etoposide. Detection of MDR-1 can play a critical role in the selection of a treatment regimen. 