<b>For testing for tumor drug resistance and resistance reversal, live tumor cells are required.</b>

Significant advances over the past 10 to 15 years in chemotherapy of some tumors such as testicular cancer and some leukemias indicates that, in spite of the undesirable side effects, chemotherapy has the potential to effect cure in the majority of patients with certain types of cancer. 

Multiple drug resistance [MDR], inherent or acquired, is one important limiting factor in extending this success to most solid tumors. By classifying individual tumors according to their specific resistance mechanisms it may be possible to define the multidrug resistance problem properly. And it may be possible to reverse such resistance.

Results from clinical trials using cyclosporin A or verapamil are encouraging, but these agents are far from ideal, and reverse resistance in only a subset of resistant tumors. Those tumors can be tested for possibilities of resistance reversal with cyclosporin A or verapamil. Proper definition of the other mechanisms of MDR, and how to antagonize them, is an urgent research priority.