Men Treated With Tamoxifen for Breast Cancer Have Higher Risk of Blood Clots

Save as Favorite
Sign in to receive recommendations (Learn more)

Men diagnosed with hormone-receptor-positive breast cancer treated with tamoxifen had more than twice the risk of developing a blood clot compared to men with a similar diagnosis who were not treated with tamoxifen, according to a study.

The research was published in the February 2019 issue of the British Journal of Cancer. Read the abstract of “Tamoxifen treatment for male breast cancer and risk of thromboembolism: prospective cohort analysis.”

Thromboembolism is the medical term for a blood clot.

Male breast cancer

While breast cancer in men is rare, it does happen. In 2019, about 2,670 new cases of invasive breast cancer will be diagnosed in men. For men, the lifetime risk of getting breast cancer is about 1 in 833.

Like breast cancer in women, breast cancer in men can be hormone receptor positive or hormone receptor negative, as well as HER2 positive or HER2 negative.

Hormone-receptor-positive breast cancer in men is treated with the same hormonal therapy medicines used to treat hormone-receptor-positive breast cancer in women.

What is hormonal therapy and how does it work?

Hormonal therapy medicines work in two ways:

  • by lowering the amount of estrogen in the body
  • by blocking the action of estrogen on breast cancer cells

There are several types of hormonal therapy medicines. Tamoxifen, a selective estrogen receptor modulator (SERM), is one of the most well-known. Tamoxifen can be used to treat premenopausal and postmenopausal women, as well as men. Tamoxifen is taken orally as a pill or a liquid. Aromatase inhibitors are another type of hormonal therapy.

In the early 2000s, the aromatase inhibitors:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

were shown to be more effective at reducing recurrence risk in postmenopausal women and are now used more often than tamoxifen to treat women who’ve gone through menopause.

Because male breast cancer accounts for about 1% of all breast cancer diagnosed, not a lot of research has been done on breast cancer in men. So it’s not clear if tamoxifen or an aromatase inhibitor is the best hormonal therapy to treat male breast cancer.

About this study

Like almost all cancer medicines, tamoxifen can cause side effects, some of them serious. Blood clots are a serious side effect of tamoxifen when it’s used to treat breast cancer in women. Little is known about the risk of blood clots in men diagnosed with breast cancer treated with tamoxifen, so researchers decided to investigate.

The study analysis included 218 men treated for hormone-receptor-positive breast cancer from May 2009 to July 2017:

  • 177 men were treated with tamoxifen
  • 41 men were not treated with tamoxifen

The men’s ages ranged from 27 to 89 years. Follow-up times ranged from 6 months to 8.4 years.

Overall, 22 men in the study developed blood clots:

  • 21 men treated with tamoxifen developed blood clots
  • 1 man who was not treated with tamoxifen developed a blood clot

The researchers’ calculations showed that men treated with tamoxifen had more than twice the risk of developing a blood clot compared to men who weren’t treated with tamoxifen.

The risk of developing a blood clot was highest during the first 18 months of treatment — 81% of the blood clots happened during this time.

Men who were older than 71 were more likely than younger men to develop a blood clot during tamoxifen treatment.

Older age was the only other factor that seemed to be linked to a higher risk of blood clots. Having a history of blood clots, heart and liver disease, and having other treatments after surgery weren’t associated with a higher risk of blood clots.

"These results will support physicians in treatment decisions of patients with male breast cancer and will sensitize them to focus their attention on the first one to two years of treatment," the researchers wrote. "In this period, an appropriate monitoring of the patients is warranted."

What this means for you

If you’re a man who has been diagnosed with hormone-receptor-positive breast cancer and hormonal therapy is part of your treatment plan, you may want to talk to your doctor about this study.

Ask your doctor how you will be monitored for blood clots, especially during the first 1.5 years of treatment.

If you’re older than 71, you may want to ask your doctor if an aromatase inhibitor may be a better hormonal therapy choice for you.

Together, you and your doctor can make the best treatment decisions for you and your unique situation.

For more information on breast cancer in men, visit the Breastcancer.org Male Breast Cancer pages.

To talk with other men who have been diagnosed with breast cancer, join the Breastcancer.org Discussion Board forum Male Breast Cancer.

Written by: Jamie DePolo, senior editor

Reviewed by: Brian Wojciechowski, M.D., medical adviser


Was this article helpful? Yes / No

Supportpeopleyellow banner mini
Back to Top