Tuesday, September 15, 2009

Targeting Cancer

If personalized medicine ever becomes widespread--and I hope it does--it will probably start with cancers.

In fact, it already has. More than ten years, ago, in 1998, the FDA approved the Genentech monoclonal antibody Herceptin (trastuzumab) as part of treatment for metastatic breast cancer--but only for patients who overexpress the membrane receptor ErbB-2 (also called HER2). For these patients, the extra copies of ErbB-2 generate signals that make the cancer spread more aggressively. The antibody binds to the receptor and diminishes this effect. But Herceptin was only shown to be effective in people who, as shown by laboratory tests, have an excess of the receptor. The approval was conditional on positive test results.

Cancers ought to be the best case for personalized medicine because treatment decisions are made by experts in the disease, based on medical tests and observations. These experts recognize that different tumors respond differently, and they are accustomed to adjusting treatment accordingly. In contrast, for many other diseases, such as mental illnesses, doctors often depend on more subjective symptoms, and patients are susceptible to the default "one size fits all" advertising of pharmaceutical companies. Cancer treatment is still the province of experts.

But it's important to ask whether those experts are doing what they need to, to get the drug to the people who will benefit, and not to the people who will not. A new article in Cancer addresses this question, and the answers are troubling.

The main complaint of the article is that there's not enough data to know. Kathryn Phillips, of the Center for Translational and Policy Research on Personalized Medicine at UCSF, and her colleagues find that in many cases there is no documentation that patients are receiving the right tests to guide their treatment. They also cite other results that

  • Perhaps two thirds of patients who could get the test to see if Herceptin would be appropriate may not get it (at least it's not recorded). By implication, many patients aren't getting a treatment that might help them.
  • A fifth of patients who do get the drug have no record of having gotten the test. This means that patients may be taking a drug, and suffering its cost and side effects, without any evidence that it will help them.
  • A fifth of the test results may be incorrect.

The argument for approving the drug was that it would make treatment cheaper and more effective. That only makes sense if the tests are given, are accurate, and are used to guide treatment. The success of personalized medicine depends on new, reliable procedures for ensuring that treatment is coupled with validated tests. If it can't be done with cancer treatment, it's hard to believe that it's a realistic goal for other diseases.

By the way, the researchers get funding for their research (said to be unrestricted) from the foundations of major health insurance companies. I'm not sure what to make of that.

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