Considering Targeted Therapies For Cancer

I first heard about STI-571 (Gleevec, a targeted cancer therapy) from a cab driver in New Orleans in 1999. “Some doctors told me there’s a new cure for leukemia,” he mentioned.

We were stuck in traffic somewhere between the airport and the now-unforgettable convention center. His prior fare, a group of physicians in town for the American Society of Hematology’s annual meeting, spoke highly of a promising new treatment. Indeed, Dr. Brian Druker had given a landmark plenary presentation on the effectiveness of STI-571 in patients with chronic myelogenous leukemia (CML) at the conference.

Since then, oncologists’ enthusiasm for targeted therapies – medications designed to fight cancer directly and specifically – has largely held. But the public’s enthusiasm is less apparent. Perhaps that’s because many people are unaware of these new drugs’ potential, or they’re put off by their hefty price tags.

Today Bloomberg News features a detailed and, I think, thoughtful story on the high cost of Sutent (sunitinib malate). This “miracle drug,” similar in many ways to Gleevec, typifies the problem of developing and providing new targeted therapies for patients with cancer. Sutent costs as much as $200 per pill, amounting to almost $50,000 per year for those who benefit. But the drug helps only a fraction of the patients for whom it’s prescribed.

So I thought I might review targeted cancer therapies, the costs-benefits issue being real and relevant. N.B.: addressing these drugs’ relative merits, effectiveness and side effects is beyond the scope of this blog. Rather, I’ll try to provide a simple framework for understanding these drugs, some information on the distinct types of new treatments and how these might work to fight cancer.

First, the framework: although many news articles consider targeted therapies together, I’d divide these in three main classes:

1. Enzyme Inhibitors. These drugs, most of which are available as pills, are designed to inhibit specific, abnormally-active signaling molecules in cancer cells. Gleevec was the first of this sort of therapy approved by the Food and Drug Administration.

2. Monoclonal antibodies. Antibodies are proteins that healthy immune cells, called B lymphocytes, generate in response to infection. Whether medicinal or native, these complex molecules circulate in the plasma component of the bloodstream. What matters to many patients is this: antibodies are given by infusion (intravenous, IV) or, rarely, by injection. Herceptin (trastuzumab) is a good example of a targeted, monoclonal antibody treatment for breast cancer.

3. Hormonal treatments. These, for the most part, target estrogen receptors in breast cancer. (I am not convinced that these are truly “targeted therapies,” but as the NCI website lists these as such, I’ll go with the flow. Femara (letrozole), a drug that reduces estrogen and other steroid levels, falls in this class.

In a forthcoming post I’ll review the small molecule-type targeted therapies for cancer that have been approved by the FDA. After that, the monoclonals. If I’m feeling brave, I may cover hormonal treatments for breast and prostate cancer.

As for traveling in New Orleans, I hope to get back there soon enough. If I do take a cab there, I wonder what news the driver will report.

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