Dr. Heath was asked how the use of predictive markers would affect trial design and implementation. He replied that, although predictive markers would have great value in stratifying patients for clinical trials, the challenge still remains to generate for these trials predictive markers that are noninvasive, such as those found in the blood or another readily accessible body fluid as opposed to the tumor, which requires an invasive biopsy. He pointed out that such noninvasive markers cannot directly detect a translocation or other genetic abnormality, but rather reflect the status of the tumor. Such reflection requires multiple-parameter measurements. Yet physicians and diagnostic companies are more familiar with single-parameter tests such as the prostate-specific antigen (PSA) test, according to Dr. Heath. “They are very uncomfortable looking at a panel of markers that goes through some computation program to give them back an answer, and I think there is a significant amount of physician retraining that has to be done to counter this,” he said.
Dr. Von Hoff asserted that Dr. Heath underestimates physicians. “We would love to work with you on this because medicine is really very pattern oriented and physicians are used to putting all those patterns into their decision-making process every day,” he said, adding the example that antibiotic sensitivity testing “is never just black and white”; physicians have to consider many parameters when selecting the appropriate antibiotic for their patients. Dr. Heath noted, however, that “diagnostic companies have been reluctant to go down this pathway, and without commercialization, you can’t get it into people’s hands.” Dr. Mills added that proper validation of predictive biomarkers through clinical trials would be a way “to reassure the practicing physician that the pattern is reproducible and does mean something effectively.”
Dr. Mills then asked Dr. Sullivan if the use of predictive markers would increase the number of patients willing to participate in cancer clinical trials. Noting he had no data to back up his opinion, Dr. Sullivan said he suspected that predictive markers would increase the number of such patient volunteers because “if patients had some sense the tests are being used to intelligently sort them out to where there might be some benefit to them and less harm, I suspect that they would find that appealing.” Patient advocate Kathy Meade of the Virginia Prostate Cancer Coalition added that predictive markers would appeal to many of the prostate cancer patients she deals with who are often interested in mechanistic explanations for the tests and treatments they receive and appreciate biomedical thinking that is “outside the box.”