The Herceptin case offers multifold lessons for personalized medicine. But perhaps the most critical of those lessons concern what might be called the sociology of diagnostics. For all its power to help doctors target treatment, the precision of molecular genetics can easily generate a residue of medical frustration. “What do you say to someone who doesn’t qualify for the drug?” asks the National Breast Cancer Coalition’s Platner. In that sense, developers of personalized medicine can inadvertently dispossess subgroups of patients. And as its power to fractionate increases, personalized medicine could have the unintended effect of creating many slivers of groups too small to warrant the economics of further drug development. One patient advocate says, “The downside is: What about something that’s very effective, but only for one percent of the patient population? Is that going to be developed?”Scientists at the National Human Genome Research Institute are exquisitely aware of the possibility of such problems. “The role of government is to work on the fragments of the patient populations that pharma isn’t going to pick up,” says one government researcher who has been participating in the development of the institute’s five-year plan. “Those discussions are still early, but that is already a concern, and it’s a real issue.”
Another collateral issue of personalized medicine is the accuracy of the diagnostic tests. Yet again, the Herceptin example offers a cautionary lesson. The first test that was developed to measure a woman’s Her-2 status typically identifies 10 to 20 percent of patients incorrectly, says Tripathy. In other words, the diagnostic was hardly definitive, and both false positives and false negatives caused a lot of frustration among breast cancer patients. Last August the FDA approved the use of an improved gene-based test for determining which patients qualify for Herceptin. The new test is “probably a little more accurate,” says Tripathy. But in that no man’s land between statistics and human emotion, the lives of many patients may be convulsed by inaccurate diagnoses. “I can foresee that happening with a lot of drugs, where the diagnostic doesn’t give a simple yes-or-no answer,” says Platner.