Targeted Therapy: Hope or Hype?

The promise and reality of targeted cancer drugs.

Here’s a quiz: Targeted drug therapy has been one of the most promising approaches to cancer treatment in the past decade. What do we mean by “targeted”?

A. A drug hits a bull’s-eye on a malignant cell; the cancer goes kablooie. 

B. Normal tissue does not contain the target. 

 We know where the target is. 

D. We know what the target is.

The answer is … all of the above. And none of the above. Which makes “targeted therapy” one of the most used and least understood phrases in the modern cancer vocabulary.

Around a decade ago, targeted therapy rose to stardom on the hope of providing powerful cancer treatment with fewer side effects than chemotherapy. It made the cover of Time magazine in 2001, and experts—those who normally talk in cautious terms—started using words like miracle.

So what is it? In its simplest sense, a targeted therapy drug is developed from scratch with the target in mind. The idea is that scientists discover a molecule critical to a tumor’s operation, but not important to normal cells, and design a medicine to short circuit that molecule. It’s kind of like stopping a car by just disconnecting the spark plugs from the engine. But the excitement also comes from what targeted therapy doesn’t do. By zeroing in on genetic flaws unique to a tumor, targeted therapy has the potential to leave normal tissue unscathed. One early report called it “a smart bomb pill.”

But after years of high expectations, reflection, and plenty of sticker shock, targeted therapy met reality. In many ways, the love affair with targeted therapy has been like any other romance. At first sight, it was new and exciting. Lots of people became starry-eyed over the possibilities. But as time passed, researchers began to see that targeted therapy was more complex and flawed than everyone first thought. The love isn’t gone, just settled.

“I think what’s happened now is we’ve grown more sophisticated,” says lung cancer specialist Martin Edelman, MD, of the University of Maryland Greenebaum Cancer Center in Baltimore, who warned in 2003 that targeted therapy would be the victim of its own press. “The whole concept of ‘targeting’ has taken on a greater degree of nuance.”

He and other researchers point out that some of the earliest cancer treatments were actually targeted therapies that came along before anyone had a catchy term for them. Women have taken the hormonal agent tamoxifen, which targets estrogen receptors in breast cancer, for four decades. Scientists didn’t understand the role of estrogen in cancer when the drug first entered the market, but that didn’t make tamoxifen any less targeted. A more traditional chemotherapy drug, Adriamycin (doxorubicin), was given to patients starting in the 1960s, even before doctors knew it disrupted a particular enzyme necessary for cell division, particularly rapidly dividing cancer cells.

“Any treatment that works hits a target,” says James Armitage, MD, a lymphoma expert at the University of Nebraska Medical Center in Omaha. “If you give somebody doxorubicin, and the cancer goes away, it’s a targeted therapy. The fact that we didn’t know the target prospectively didn’t change that.”

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