Doctors may start running genetic tests before writing prescriptions

The New York Times has an interesting article on the genetic component behind how useful (or not) several popular prescriptions are. The main focus of the article is tamoxifen, a cancer drug which is a (relatively) inexpensive and effective alternative to a newer class of cancer drugs called "aromatase inhibitors."

Tamoxifen itself isn't what kills the cancer cells. It is converted by the body into endoxifen, which is the substance that actually fights cancer. However, researchers recently showed that not everyone has the genetic component which is required to make the conversion. The conversion is done by an enzyme called 2D6, and "up to 7 percent of people" do not produce this enzyme. Another 20 to 40 percent of people produce a low level of the enzyme, which may not be enough to convert tamoxifen at an effective rate.

Genetic testing can determine whether a person is producing enough 2D6 to make tamoxifen treatment useful. And more studies are showing that this is true of a lot of other medications, as well.

Most drugs do not treat 100% of patients 100% of the time. They have varying success rates, and for a long time no one really knew what caused the variation. Is it possible that DNA testing could provide an answer to the mystery?

Last year, a European regulatory agency determined that the new colon cancer drug Vectibix wasn't effective enough to warrant official approval. The drug's manufacturer, Amgen, went back to the lab and found that a specific genetic mutation in the tumor determined whether or not Vectibix would be effective.