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Protective Tamoxifen May Lead to Earlier Diagnosis of Hormone-Receptor-Negative Cancer

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Tamoxifen is used to lower the risk of hormone-receptor-positive breast cancer in certain women with a higher-than-average risk of disease, but who've never been diagnosed. A study wanted to see if tamoxifen had an effect on when breast cancer was diagnosed.

This study found that women at high risk who took tamoxifen and developed hormone-receptor-NEGATIVE breast cancer had the cancer diagnosed earlier compared to women who didn't take tamoxifen. (Tamoxifen doesn't reduce the risk of hormone-receptor-negative breast cancer.) Earlier diagnosis can mean that the cancer is less advanced and more treatable.

The researchers aren't sure how tamoxifen led to earlier detection of hormone-receptor-negative cancers.

Tamoxifen is a selective estrogen receptor modulator (SERM), a type of hormonal therapy medicine. SERMs affect the estrogen receptors in different kinds of cells in different ways. For example, tamoxifen activates the estrogen receptors in bone cells, which makes bones stronger. Tamoxifen has the opposite effect on breast cells -- it blocks the estrogen receptors in breast cells. Blocking the estrogen receptors blocks the effects of estrogen, which slows or stops the growth of breast cells, including any breast cancer cells with estrogen receptors.

Tamoxifen's estrogen-blocking ability helps reduce the risk of hormone-receptor-positive breast cancer in women at high risk who've never been diagnosed. Tamoxifen also is used to reduce the risk of hormone-receptor-positive breast cancer coming back and to reduce the risk of a new cancer developing in the other breast. Tamoxifen isn't used to treat or lower the risk of hormone-receptor-negative breast cancer. Hormone-receptor-negative breast cancers don't have hormone receptors, so there is nothing for tamoxifen to block.

A very large study called the Breast Cancer Prevention (BCP) trial showed that tamoxifen can lower the risk of hormone-receptor-positive breast cancer by 50% in high-risk women who had never been diagnosed. The BCP trial involved more than 13,000 high-risk women. About half of the women got tamoxifen. The other women got a placebo (sugar pill). All of the women received intensive breast cancer screening, including frequent mammograms.

The researchers conducting the study reviewed here looked at the medical records of the women in the BCP trial. During the 5 years of follow-up in the BCP trial:

  • 174 women were diagnosed with hormone-receptor-positive breast cancer
  • 69 women were diagnosed with hormone-receptor-negative breast cancer

The researchers looked at the length of time between when the women enrolled in the BCP trial and when they were diagnosed. They figured out a "median time" until diagnosis. Median time means that half the women were diagnosed earlier than the median time and half the women were diagnosed later than the median time.

Among women diagnosed with hormone-receptor-POSITIVE breast cancer, median time until diagnosis was:

  • 43 months for women who got a placebo
  • 51 months for women who got tamoxifen

This difference was probably due to chance and not because the two groups received different medicines.

Among women diagnosed with hormone-receptor-NEGATIVE breast cancer, median time until diagnosis was:

  • 36 months for women who got a placebo
  • 24 months for women who got tamoxifen

This difference was statistically significant, which means that it was likely due to the effects of tamoxifen and not just to chance.

Though the researchers aren't sure why tamoxifen resulted in an earlier diagnosis of hormone-receptor-negative breast cancer, they suspect it might have something to do with breast density. Tamoxifen can make breast tissue less dense. This means that there is relatively more fatty tissue than non-fatty tissue in the breast. It's easier to see breast cancers on a mammogram when the breast is less dense.

If you're at higher-than-average risk for breast cancer, based on your family or medical history, you want to do all that you can to keep your risk as low as possible. Talk to your doctor about all your options, including diet, lifestyle, and exercise choices, as well as medical and surgical options. If you haven't been diagnosed, tamoxifen is one medical option you and your doctor may consider to lower your risk of hormone-receptor-positive breast cancer. You and your doctor also will develop a breast cancer screening plan that is right for you. This may include getting both mammograms and breast MRIs, as well as more frequent screening.

The Lower Your Risk section has detailed information on the medical and surgical options you and your doctor might consider.

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