The Trouble With Targeted Therapies

Gina Kolata has a great piece today in The New York Times about the imperfect tests that are used to determine whether expensive, "targeted therapy," should be used as a cancer treatment.

The story's lede anecdote involves Dr. Linda Griffith, director of the Center for Gynepathology Research at MIT, who has breast cancer. Kolata writes that the complications began for Dr. Griffith when "she had a test to see whether her tumor had extra copies of a protein, HER2. If it did, it would respond to a drug, Herceptin, which blocks the protein and stymies the tumor’s growth." The piece continues:

Drugs aimed at disabling proteins that spur cancer are, many oncologists say, the future of cancer therapies. Only a few are available now but almost every new drug under study is designed to disable cancer-fueling proteins.

But these so-called targeted therapies are only as good as tests to find their protein targets. And while most patients do not yet know it, those tests can be surprisingly unreliable.

Acknowledging the problem, cancer specialists on Monday announced new testing guidelines for one protein target, but as new targets are identified, the problem continues to grow.

Not only do the tests give false positives about 20% of the time (and false negatives 5-10% of the time), they are often interpreted differently at different labs, the story says. As it turns out, part of Dr. Griffith's tumor tested positive and the rest negative. Ultimately, she decided not to take the drug, Herceptin, which costs more than $40,000 a year wholesale and can have a rare, serious side effect: severe heart damage that can be fatal.