Ten Years of Tamoxifen Works Better to Lower the Risk of a Breast Cancer Recurrence

ASCO Annual Meeting
June 2, 2013

A recent study comparing five or 10 years of tamoxifen (Nolvadex, Soltamox) therapy for early-stage, estrogen receptor (ER)-positive breast cancer showed that continuing tamoxifen for longer than five years further lowers the risk of a breast cancer recurrence (return of the cancer) and death. ER-positive breast cancer uses the hormone estrogen to grow and spread. Tamoxifen is a type of hormonal therapy that blocks the effects of estrogen on tumor growth and has been proven to lower the risk of a breast cancer recurrence and lengthen the lives of women with early-stage breast cancer. Currently, the standard length of tamoxifen therapy is five years, and women start it right after finishing surgery or chemotherapy.

This study included 6,953 women in the United Kingdom who had been taking tamoxifen for five years and then either stopped taking the drug or continued for an additional five years. Researchers found that both recurrences and deaths decreased with each year of continuing tamoxifen, and the women with the lowest risk of recurrence were those who took tamoxifen for more than nine years. Among the women who took tamoxifen for 10 years, about 17% had a recurrence, compared with 19% of those who took the drug for five years. Longer treatment also lowered the risk of dying from breast cancer. Researchers estimate that, compared to taking no tamoxifen, taking tamoxifen for 10 years reduces the deaths from breast cancer by a third in the first 10 years after diagnosis and by half in later years.

What this means for patients

“Five years of tamoxifen is already an excellent treatment, but we thought that longer treatment might be even better because women with ER-positive breast cancer can have recurrences long after treatment is completed. Until now, though, there have been doubts whether continuing tamoxifen beyond five years is worthwhile,” said lead study author Richard G. Gray, MA, MSc, Professor of Medical Statistics at the University of Oxford in the United Kingdom. “This study and a related international study confirm that there is definitely a survival benefit from longer tamoxifen treatment, and many doctors will likely recommend continuing tamoxifen for an extra five years.”

The side effects of tamoxifen also increased with longer use. These side effects are similar to menopausal symptoms. They include night sweats, hot flashes, and rare but serious side effects, such as a higher risk of uterine cancer, blood clots, and stroke. In this study, the risk of stroke was not higher for women taking tamoxifen for 10 years, but the risk of uterine cancer was higher. However, the researchers estimate that for every extra uterine cancer that occurs as a side effect of long-term tamoxifen, 30 deaths from breast cancer would be prevented.

Questions to Ask Your Doctor

  • What stage of breast cancer do I have? What does this mean?
  • What is my hormone receptor status?
  • What are my treatment options?
  • After treatment is over, what are my options to lower my risk of a breast cancer recurrence?
  • What are the risks and benefits of each option?

For More Information

Guide to Breast Cancer

What to Know: ASCO’s Guideline on Hormonal Therapy for Hormone Receptor-Positive Breast Cancer

Menopausal Symptoms

Managing Side Effects