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What Is the Connection between Tamoxifen and Uterine Cancer?

Dan Harkins
By Dan Harkins
Updated May 17, 2024
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The prescription drug tamoxifen has been used since 1998 to treat breast cancer patients by restricting the body's production of estrogen, which tumors need to thrive. Going by the brand names Nolvadex®, Valodex® and Istubal®, this medication has some side effects, including the development of cancers in the uterus of some women. Tamoxifen and uterine cancer rarely go together; studies show, however, that using another breast cancer drug called raloxifene could be a safer choice.

Both men and women are prescribed tamoxifen after being diagnosed with breast cancer. Surgical excision is also commonly used to remove tumors. Some women with a genetic predisposition for breast cancer, however, have been prescribed the medication to help stem estrogen levels in an attempt to keep tumors from growing at all.

Some side effects go along with a regular regimen of tamoxifen and uterine cancer, blood clots and even strokes are among the more severe. Other major symptoms may include chest pain, numbness, migraines, confused thinking, bodily swelling, nausea, irregular vaginal blood, uterine pain, problems seeing, flu-like symptoms and even a newly arrived lump in the breast. An allergic reaction to the drug could cause trouble breathing and swelling of the face and neck. A doctor should be consulted immediately if any of these side effects are experienced.

In 1999, an in-depth Study of Tamoxifen and Raloxifene (STAR) revealed that raloxifene is equally effective at suppressing estrogen and preventing breast cancer development. Though the incidences are low when patients take tamoxifen and uterine cancer develops — just 36 women out of a total of 4,732 study patients, the prevalence was 36 percent lower for those who took raloxifene instead — just 23 of 4,712. Women who took tamoxifen also were 29 percent more likely to develop a blood clot; however, the number of heart attacks and strokes was the same for both groups.

Ties have been made between tamoxifen and uterine cancer of two varieties. The first is called endometrial cancer, which strikes two of every 1,000 women taking tamoxifen, and just one of every 1,000 women not taking medication. The other type of pelvic cancer, called uterine sarcoma, also was slightly higher for those prescribed tamoxifen; however, less than one in 1,000 people in both groups were likely to develop it.

Raloxifene was released in 1997 for the treatment of osteoporosis — just a year before tamoxifen. The former drug later proved to be effective in reducing breast cancer too. For women between 60 and 64 years old, nearly two in every 100 are likely to develop breast cancer in five years.

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