Why Gene Tests for Cancer Don’t Offer More Answers

From Scientific American:

In the intervening decades, researchers have come to recognize that most cancers are driven largely by abnormalities in genes. Genetic analysis of tumors has, therefore, become standard practice for many malignancies—such as breast, lung and colon cancer—because the information may help guide therapy. Clinicians have amassed a modest arsenal of drugs able to counteract some of the most common mutations.

Yet many patients learn that their cancers have mutations for which no drug exists. In fact, the roles many of these genetic changes play in cancer growth are poorly understood. Complex analyses of DNA done across a range of cancer types have revealed a landscape rife with genetic mutations, and very little of this encyclopedic information is helping doctors to make treatment decisions. To date, the U.S. Food and Drug Administration has approved just 29 tests for specific mutations that can directly influence therapy.

Several major research collaborations are now making heroic efforts to identify more mutations that can serve as drug targets and to collect the information that will allow doctors to match many more patients with such targeted therapies. And earlier this year President Barack Obama announced the National Cancer Moonshot, a $1-billion initiative that includes funding for such efforts. The task is so large and complicated, however, that the gap between genetic knowledge and patient benefit is likely to widen for some time before the promised revolution in care becomes a reality for most people afflicted by cancer. “We’re in a transition period,” says Stephen Chanock, who directs the Division of Cancer Epidemiology and Genetics at the National Cancer Institute.

The genetic changes that eventually trigger cancerous growth fall into two main groups. First, there are hereditary germ-line mutations, which people inherit from their parents. Second, there are somatic mutations, which arise over the course of one’s life as a …

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