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Study Finds Benefit for Breast Cancer Patients to Take Tamoxifen for 5 Years

A large study finds that women with early-stage breast cancer who take tamoxifen for five years have less risk that their cancer will return compared to women who take the drug for two years. According to Cancer Research UK, a British charity organization that funded the study, for every hundred women who completed the full five year course of tamoxifen, the cancer came back in around six fewer women.

Tamoxifen is a drug taken orally in pill form. For over a quarter of a century, physicians have prescribed tamoxifen to help treat patients with advanced breast cancer. In the 1990s, physicians began using tamoxifen to treat early stage breast cancer after breast surgery (lumpectomy or mastectomy). Tamoxifen has been shown to help prevent the original breast cancer from returning after breast surgery while also hindering the development of new cancers in the opposite breast

To grow and reproduce, breast cancer cells require the female hormone estrogen. Tamoxifen is an "anti-estrogen" and works by competing with estrogen to bind to estrogen receptors in breast cancer cells. Tamoxifen is formally known as a selective estrogen receptor modulator (SERM). By blocking estrogen in the breast, tamoxifen helps slow the growth and reproduction of breast cancer cells.

Earlier studies have shown that taking tamoxifen for five years may be beneficial for women with early-stage breast cancer. According to Cancer Research UK, the current study is the first large study to compare the long-term benefit of five years of tamoxifen versus two, over a ten-year follow-up period.

Of the nearly 3,500 patients took part in the study, the cancer came back in around 40 per cent of the women who took tamoxifen for five years, compared to 46 per cent among those who took it for two years. The study was published in the March 21, 2011 issue of the Journal of Clinical Oncology.

“Our study provides conclusive evidence that taking tamoxifen for five years offers women the best chance of surviving breast cancer,” said senior author Dr Allan Hackshaw, in a Cancer Research UK press release. “Women diagnosed with early stage breast cancer who are prescribed tamoxifen are recommended to take the drug for five years, but we know that many stop after two or three. Worryingly, our results suggest that by doing this, they could increase their risk of cancer coming back.”

Tamoxifen has been associated with a number of side effects. The most common side effect of tamoxifen is a higher occurrence of hot flashes. Other side effects include irregular menstrual cycles, unusual vaginal discharge or bleeding, and irritation of skin around the vagina. Tamoxifen does not cause menopause in pre-menopausal women, though its side effects may mimic menopausal symptoms. Tamoxifen also increases a woman's chances of developing serious health problems including:

  • endometrial cancer (cancer of the lining of the uterus)
  • deep vein thrombosis (blood clots in large veins, particularly in the legs)
  • pulmonary embolism (blood clot in the lung)
  • possibly stroke

However, in the current study, an additional benefit of taking tamoxifen for five years was that it was found to reduce the risk of developing or dying from heart disease. According to Cancer Research UK, this benefit was greatest in women aged 50-59 at diagnosis. Among that age group, 35 percent fewer women developed a heart condition and there was a 60 percent reduced risk of death.

 “Ours is the first large study to look at the long-term benefits of five years of tamoxifen and show it has the extra benefit of substantially reducing a woman’s risk of developing heart disease, said Dr. Hackshaw, in the Cancer Research UK press release. “This effect was greatest among women in their 50s, perhaps because the way plaques tend to build up in the arteries with age may be easier for tamoxifen to reverse in younger women.”

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