December 19th, 2005

Breast Cancer Treatment with Tamoxifen not as effective for all Women

Tamoxifen

Tamoxifen can greatly reduce the risk of cancer relapse; however there may be some women who have a genetic variation that will make it less effective. Researchers at the Mayo Clinic, Rochester, Minnesota found that a genetic variance changes the effectiveness of tamoxifen.

Matthew Goetz, MD, from the Department of Oncology, reported in the December 20^th issue of the Journal of Clinical Oncology that one in 10 women in the U.S. have the variation of the level of cytochrome P4502D6 (or CYP2D6) which is a liver enzyme that is important for metabolizing tamoxifen.

The women who have the modified CYP2D6 gene have a higher risk of a relapse of breast cancer when treated with tamoxifen for over a five year period. Most of the time the tamoxifen will reduce the risk of a recurrence by nearly half for women who have estrogen-receptor positive type breast cancer. The women that had the genetic modification did not have the hot flashes that are typically a side effect of taking the tamoxifen.

They conducted a study of 223 women that were affected with estrogen-receptor positive breast cancer by studying tumor and tissue samples. Of these women 137 had the modified CYP2D6 gene on chromosome 22 of both copies. There were 40 women that had only one chromosome modified.

The women who were homozygous for the variant had twice the likelihood of the cancer returning. This research will help in treat women who have been diagnosed with estrogen-receptor positive breast cancer.