Gene Testing May Be Key for Treating Some Women with Breast Cancer

Strategic Insights -

Researchers at the Mayo Clinic have made a new discovery that could be crucial for treating some women with breast cancer. The study found that women with an inherited deficiency in the CYP2D6 gene have a nearly fourfold higher risk of early breast cancer recurrence compared to women who do not have the deficiency. This is because the CYP2D6 gene is important for the metabolism of tamoxifen, a hormone therapy used to prevent the development of estrogen-receptor-positive breast cancer and to stop it from coming back.

Key Takeaways:

  • Women with an inherited deficiency in the CYP2D6 gene have a nearly fourfold higher risk of early breast cancer recurrence compared to women who do not have the deficiency, which translates to a 3.8-fold increase in risk of developing breast cancer recurrence.
  • The study suggests that postmenopausal patients being considered for tamoxifen therapy should be tested for CYP2D6 before beginning therapy.
  • Women with poor metabolizers of CYP2D6 may have a higher risk of breast cancer recurrence if they stay on tamoxifen, but switching to anastrozole may help reduce this risk.
  • The researchers demonstrated that among patients who switched to anastrozole, there was no increased risk of breast cancer recurrence for CYP2D6 poor metabolizers in years three to five.
  • The study highlights the emerging science of pharmacogenomics, which involves studying genetic differences in how patients metabolize or process drugs to individualize therapy.

Statistics:

  • Nearly 3,900 women were treated in the ABCSG-8 study, which randomly assigned women to either tamoxifen therapy for five years or tamoxifen for two years followed by three years of anastrozole.
  • 25% of the tumors examined in the study had high expression of both HOXB13:IL17BR and molecular grade index, which led to a nearly threefold higher risk of recurrence elsewhere in the body.
  • The benefit of switching to anastrozole was most pronounced in the group of patients with deficient CYP2D6 metabolism, with 40% reduced risk of breast cancer recurrence compared to staying on tamoxifen.

Sources:

  • "Gene Testing May Be Key for Treating Some Women with Breast Cancer" by Mayo Clinic, jointly announced with the Austrian Breast and Colorectal Cancer Study Group (ABCSG) News Release, 2008.
  • Study conducted by Mayo Clinic and ABCSG, presented at the Cancer Therapy & Research Center-American Association for Cancer Research (CTRC-AACR) 31st annual San Antonio Breast Cancer Symposium, 2008.
  • Dr. Matthew Goetz, M.D., lead investigator, and Dr. Michael Gnant, M.D., professor of Surgery at the Medical University of Vienna, Austria, and president of ABCSG, quoted in the news release.