The Weisenthal Cancer Group has announced that clinical data presented at the annual meeting of the American Society of Clinical Oncology (ASCO) show that its new laboratory test accurately identified patients who would benefit from treatment with the molecularly-targeted anti-cancer therapies gefitinib (Iressaâ, AstraZeneca) and erlotinib (Tarcevaâ, Genentech). The new test, called the EGFRxä assay, predicted accurately survival of patients treated with the targeted drugs. The EGFRxä test, which can also be applied to many emerging targeted cancer drugs, could help to solve the growing problem of determining which patients should receive costly, new treatments that can have harmful side effects and that work for some but not all cancer patients who receive them.
Larry Weisenthal, MD, PhD, a medical oncologist and developer of the EGFRxä assay explains that the new test relies on “whole cell profiling” in which living tumor cells are removed from an individual cancer patient and exposed in the laboratory to the new drugs. A variety of metabolic and apoptotic measurements are then used to determine if a specific drug was successful at killing the patient’s cancer cells. The whole cell profiling method differs from other tests in that it assesses the activity of a drug upon combined effect of all cellular processes, using several metabolic and morphologic endpoints. Other tests, such as those which identify DNA or RNA sequences or expression of individual proteins often examine only one component of a much larger, interactive process.
According to Weisenthal, this may explain why EGFRx whole cell profiling is the only test to date to demonstrate a statistically significant association between prospectively reported test results and patient survival. Using the EGFRxä assay and the whole cell profiling method, Weisenthal’s group correlated test results, which were obtained by his lab and reported to physicians prior to patient treatment, with significantly longer or shorter overall patient survival depending upon whether the drug was found to be effective or ineffective at killing the patient’s tumor cells in the laboratory. Patients prospectively identified by Weisenthal as favorable candidates averaged 485 days of life after treatment with the targeted therapy drugs. In contrast, patients identified as unfavorable candidates for the drugs averaged 75 days survival after receiving the drugs. This compares to 76 days average survival among patients identified as unfavorable candidates and who did not receive a targeted therapy drug. Survival among patients identified by Weisenthal as unfavorable candidates was therefore similar regardless of whether or not they received the targeted drugs.
These so-called “smart drugs” focus their effects on specific, identifiable processes occurring within cancer cells. The new drugs are highly promising in that they sometimes provide benefit to patients who have failed traditional therapies. However, they do not work for everyone, they often have unwanted side effects, and they are all extremely expensive: some cost patients and insurance carriers $5,000 to $7,000 or more per month of treatment. Patients, physicians, insurance carriers, and the FDA are all calling for the discovery of predictive tests that allow for rational and cost-efficient use of these drugs.