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Tamoxifen use reduces breast cancer risk

Tamoxifen also reduced hip, spine and radius fractures by 32% compared with placebo.

Issue: March 1, 2006

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Tamoxifen appears to reduce breast cancer and osteoporotic fractures, according to an update from the National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention (P-1) Study.

“Because women with a history of LCIS (lobular carcinoma in situ) or atypical hyperplasia have a high risk of developing invasive breast cancer, women in this group also have the potential for demonstrating a positive benefit-risk ratio from tamoxifen,” said Bernard Fisher, MD, from the University of Pittsburgh. “The high breast cancer risk among women with such a history is evident from the P-1 population, for whom the initial report found a breast cancer incidence rate of 12.99 per 1,000 in women with LCIS and 10.11 per 1,000 for those with atypical hyperplasia.

“The net benefit achieved with tamoxifen varied according to age, race and level of breast cancer risk. Although not all patients had a net benefit, it was clearly evident that there were many women who demonstrated such a benefit,” Fisher told Hem/Onc Today.

Benefit of tamoxifen

Beginning in 1992, researchers randomized 13,388 women in a double-blinded study: 6,681 received 20 mg of daily tamoxifen and 6,707 received placebo. Findings from 1998 revealed that tamoxifen reduced the risk of estrogen-receptor–positive tumors and osteoporotic fractures in women at an increased risk for breast cancer.

Following these positive data, researchers unblinded the study. Patients in the placebo arm chose to remain on placebo or cross over to tamoxifen.

Prior to study enrollment, patients underwent mammography to determine the presence of breast cancer. Researchers excluded patients with breast cancer from enrollment. Other exclusion criteria included the use of hormone replacement therapy, oral contraceptives or androgens within three months of randomization, a history of deep venous thrombosis or a history of pulmonary embolism.

Researchers stratified patients according to age, race, history of LCIS and atypical hyperplasia and their five-year predicted breast cancer risk.

Protective effect

There were 13,207 women involved in the follow-up analyses. Most were white and were aged between 40 and 59. More than 75% of patients reported having at least one first-degree relative with breast cancer.

At a follow-up of seven years, the cumulative rate of invasive breast cancer was reduced by 43%: from 42.5 cases per 1,000 women in the placebo group to 24.8 cases per 1,000 women in the tamoxifen group (P < .001), according to the study. Tamoxifen use reduced noninvasive breast cancer — ductal carcinoma in situ and LCIS — by 37%.

“Tamoxifen reduced the risk of invasive breast cancer in women in all subgroups defined by age, history of LCIS, history of atypical hyperplasia or level of predicted risk of breast cancer,” Fisher wrote in the Journal of the National Cancer Institute.

The protective effect of tamoxifen was most pronounced between the second and fifth years of use. The rate of breast cancer incidence remained relatively constant throughout the seven-year follow-up period. There was a decreased risk of breast cancer in the placebo group after six years because, after the study was unblinded, women in the placebo group crossed over to tamoxifen.

In addition to protecting against cancer, tamoxifen reduced hip, spine and radius fractures by 32% compared with placebo. However, researchers reported that prolonged tamoxifen use has been associated with adverse events such as an increased risk of endometrial cancer and an increased risk of pulmonary embolism in women over 50. – by Rebekah Cintolo

Editor’s note: These astonishing data are probably underestimates as many pulmonary emboli are missed if autopsies are not performed. That is woefully the case in the United States. - Harry S. Jacob, MD, FRCPath(Hon)

For more information:

• Fisher B, Costantino JP, Wickerham DL, et al. Tamoxifen for the prevention of breast cancer: current status of the National Surgical Adjuvant Breast and Bowel Project P-1 study. J Natl Cancer Inst. 2005;97:1652-1662.