Tamoxifen chemoprevention associated with earlier diagnosis of ER-negative breast cancer

Women at elevated risk of breast cancer who had been randomly assigned to tamoxifen treatment and then developed estrogen receptor (ER)–negative breast cancer were diagnosed earlier than women who had been randomly assigned to take a placebo and then developed ER-negative disease, according to a study published online October 7 in the Journal of the National Cancer Institute. Tamoxifen has been shown to reduce the risk of ER-positive breast cancer in women at high risk of disease. The drug does not alter the risk of ER-negative disease.

In the current study, Yu Shen, Ph.D., of the University of Texas M. D. Anderson Cancer Center in Houston and colleagues performed a retrospective analysis of the Breast Cancer Prevention Trial to determine whether tamoxifen affected the time to breast cancer diagnosis. A total of 13,388 women at high risk of breast cancer participated in the trial and were randomly assigned to treatment with tamoxifen or placebo. During the follow-up period, 174 women were diagnosed with ER-positive tumors and 69 women with ER-negative tumors.

The median time to diagnosis with ER-positive disease was similar in the placebo and tamoxifen groups at 43 and 51 months, respectively. The median time to diagnosis for women with ER-negative disease did differ in a statistically significant manner between the two groups, at 36 months in the placebo arm and 24 months in the tamoxifen arm.

The researchers conclude that although tamoxifen does not alter the risk of ER-negative disease in high risk women, it may advance detection of the disease. "We showed that tamoxifen treatment appeared to shorten the time to diagnosis of ER-negative breast cancer by approximately 1 year but was not associated with the time to diagnosis of ER-positive breast cancer," the authors write.

The reason for the difference in time to diagnosis of ER-negative tumors in the two treatment arms is not clear. However, the authors hypothesize that the drug makes the tumors more detectable. They do not see evidence that tamoxifen altered the growth rate of ER-negative disease because they did not see an increase in the rate of these tumors or a higher incidence in younger women during the follow-up period. The observation should be further investigated, they conclude.

Source: Journal of the National Cancer Institute