Tamoxifen may affect time to first diagnosis of ER-negative breast cancer

Although tamoxifen does not reduce the incidence of ER–negative breast cancer, it may lead to the advanced detection of such tumors by about 1 year when compared with non–tamoxifen-treated tumors. Tamoxifen did not appear to affect the time to diagnosis of ER-positive tumors.

The researchers used data from the randomized, placebo-controlled Breast Cancer Prevention Trial (BCPT) to determine whether tamoxifen had an effect on the time to first diagnosis of breast cancer. A total of 13,388 women were enrolled in BCPT: 174 with ER-positive tumors and 69 with ER-negative tumors.

The median times to diagnosis of ER-positive tumors were similar in both treatment groups: 43 months for the placebo arm and 51 months for the treatment arm. Times to diagnosis of ER-negative tumors, however, differed between treatment groups, with median times to diagnosis of 36 months in the placebo arm vs. 24 months in the tamoxifen arm (95% CI, 3-17 months). ER-negative breast cancers in the tamoxifen arm were more likely than those in the placebo arm to be detected by mammography than by clinical breast examination alone after adjustment for age and tumor size (OR=4.68; 95% CI, 0.86-25.32). No differences were found in the mammography detection rates for ER-positive tumors by treatment arm.

A notable limitation of the study was that breast density was not assessed in the BCPT. Furthermore, the number of ER-negative tumors diagnosed was small, so conclusions based on these data should be interpreted with caution, the researchers wrote.

J Natl Cancer Inst. 2008;100:1448-1453.