In the event of recurrence after chemotherapy, they can help to identify a different therapy. If a clinical trial is under consideration, these tests can identify the specific clinical trial in which the odds for success are the greatest. In more than 1500 world wide studies in the past decade, it was shown that patients treated with assay-favored drugs were, on the average, seven times more likely to respond to treatment. However, this does not mean that every patient will respond to a laboratory assay-favored drug, and there is no guarantee that a drug will be found that shows activity against the cancer cells of a particular person. The tests reveal, but cannot alter, an individual s resistance to drugs.
Drug resistance is the principal reason for the failure of chemotherapy.
Some tumors are highly resistant to virtually all anti-cancer drugs, while other tumors are quite sensitive. Most patients tumors fall in between these two extremes, with resistance to some drugs but not to others. Many mechanisms by which cancer cells develop resistance have been identified. Most cancers have some degree of drug resistance with many patients not responding to the chemotherapy most commonly prescribed for the tumor type. DRAa is a laboratory test that measures the ability of pharmaceuticals and other therapies to stop cancer cells from dividing and growing.