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Pharmacogenetics: A Growing Area for Genetic Testing

by Sue Friedman and Lisa Kessler

Genetic testing is a rapidly-growing field that is providing researchers with new ways to apply testing to cancer treatment and prevention. Pharmacogenetics is one emerging area of genetics that looks at how individuals metabolize (activate or inactivate) medications.

What is intuitive to most of us, that people react differently to medications, is now being proven by genetic research. Just as genes like BRCA can help determine our chances for getting cancer, other genes, like CYP2D6, affect how our bodies change and clear medications. According to recent research on tamoxifen, 7-10 percent of women with breast cancer have a special variant of the CYP2D6 gene (also called 2D6), that may reduce the effectiveness of tamoxifen.

A genetic test requiring only a cheek swab can identify a woman’s 2D6 genetic status. The Tamoxifen 2D6 test is currently only appropriate for postmenopausal women who are taking or considering taking tamoxifen to prevent the recurrence of breast cancer. Knowing their genetic status, women can work with their physicians to identify whether alternative treatments, such as aromatase inhibitors, may be more effective for them.

Lisa Kessler is a board-certified genetic counselor with a background in cancer genetic counseling and research.

Who Qualifies For 2D6 Testing?

2D6 testing is available only for postmenopausal women who are taking or considering taking tamoxifen to prevent the recurrence of breast cancer. This test is not appropriate for:

  • Women who are pre- or perimenopausal. No alternative treatment options are as effective as tamoxifen. (This may change as researchers learn more about 2D6 and tamoxifen.)
  • Women with hormone-negative cancers. Tamoxifen is only recommended as a treatment for hormone-positive cancers.
  • High-risk women who have not had breast cancer. There is not enough data about this situation to make recommendations at this time. (This may change as researchers learn more about 2D6 and tamoxifen.)

References

MP Goetz, JM Rae, VJ Suman, et al. Pharmacogenetics of tamoxifen biotransformation is associated with clinical outcomes of efficacy and hot flashes. Journal of Clinical Oncology, December 2005; Volume 23, no. 36: p 9312-93128.

SK Knox, JN Ingle, VJ Suman, et al. Cytochrome p450 2D6 status predicts breast cancer relapse in women receiving adjuvant tamoxifen. Proceedings of The American Society of Clinical Oncology, June 2006; Volume 24, no. 18S: abstract 504.

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