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Tamoxifen Cuts Time to Breast Cancer Detection

CancerWise - December 2008

The anti-hormonal drug tamoxifen can make estrogen receptor-negative (ER-negative) breast cancer easier to diagnose, although it does not prevent or treat the disease.

Researchers at M. D. Anderson published these findings in the Oct. 1 Journal of the National Cancer Institute.

Significance of results

Women at high risk for breast cancer who took tamoxifen as a preventative measure and later developed ER-negative breast cancer were diagnosed an average of 24 months after taking the drug. This is a full year sooner than women who took placebos (a pill that has no effect on the body) and were later diagnosed with ER-negative breast cancer.

While measuring long-term survival was not part of the study, researchers say the one-year-earlier diagnosis is an unexpected and significant finding that may have a lifesaving impact.

“Based on our basic understanding of breast cancer, cure rate is higher when cancer is detected at an earlier stage and treated properly,” says lead author Yu Shen, Ph.D., professor in M. D. Anderson’s Department of Biostatistics. “Our findings open up a new area of research.”

Tamoxifen is an anti-hormonal therapy known to be effective against ER-positive breast cancer, which is driven by the hormone estrogen.


The Breast Cancer Prevention Trial (BCPT), previously conducted at 300 locations, found tamoxifen reduces the incidence of ER-positive breast cancer.

Other research indicated ER-negative breast cancer is less likely to be found by mammograms than ER-positive breast cancer.

Mammography detected ER-negative tumors in:

  • 77.5% of women who took placebos
  • 94.8% of women who took tamoxifen

Research methods

Using a new, more flexible statistical model, scientists examined the BCPT data to find if tamoxifen affected the length of time until breast cancer was diagnosed and the method of detection. These had not been determined in the original BCPT study. 

“It’s a good example of how innovative application of statistical methods can make a great contribution to better understanding the biological mechanisms of cancer,” Shen says.

Primary results

Researchers examined the statistics for ER-positive breast cancer.

They found tamoxifen:

  • Did not make a difference in the length of time before diagnosis
  • Did reduce the incidence of the disease

They also looked at the results for ER-negative breast cancer.

They found tamoxifen:

  • Reduced the median time to breast cancer diagnosis by a year 
  • Did not reduce incidence of the disease

What’s next?

Researchers provided a few hints about why tamoxifen treatment might make ER-negative cancers easier to detect, but Shen says pinpointing the biological factors behind the finding will require additional research.

"As statisticians, we uncover the phenomenon, but we cannot explain why it happened," she says.

Tamoxifen therapy alters breast density, which appears to be a major factor determining the sensitivity of mammography screening, the authors note. By altering the density of normal tissue, the drug may modify the contrast between normal tissue and tumors, perhaps increasing the ability of mammography to detect disease.

The BCPT trial did not collect breast-density data, so this risk factor could not be evaluated.

© 2015 The University of Texas MD Anderson Cancer Center