ASCO Recommends Tamoxifen for up to 10 Years

Harold Burstein, MD, PhD

Harold Burstein, MD, PhD

Women with hormone receptor-positive (HR+) breast cancer should be given the option to have adjuvant hormonal therapy for as long as 10 years, according to new guidelines issued today by the American Society of Clinical Oncology (ASCO).

The updated guidelines reflect results from several large studies that showed women who took tamoxifen for 10 years had a lower risk of recurrence and a “survival advantage,” compared to women who took the drug for only five years.

In a press release issued by ASCO, Harold J. Burstein, MD, PhD, a breast oncologist with the Susan F. Smith Center for Women’s Cancers at Dana-Farber, explained “tamoxifen taken for five years has been the standard adjuvant hormonal treatment for decades, but we now have evidence to recommend up to 10 years of tamoxifen for women with hormone receptor-positive breast cancer.” Burstein is co-chair of ASCO’s Expert Panel that wrote the guideline update.

The update applies to pre-/peri- and post-menopausal with HR+ breast cancer. However, the guidelines also state that post-menopausal women who have completed five years of tamoxifen should have the option to continue another five years of treatment with either tamoxifen or an aromatase inhibitor.

Before starting any treatment, Burstein notes that women should discuss with their physician the potential risks and benefits of adjuvant hormonal therapy for extended periods of time.

More details on the ASCO guidelines are available here. For more information on breast cancer treatment, visit the Susan F. Smith Center Breast Oncology Program website. 


  1. Does this recommendation apply to men who have he breast cancer and are taking Tamoxifin?

    • Dear Alan–
      Thank you for your comment. This guideline only applies to women; men should take 5 years of tamoxifen.
      Thank you again for connecting with us and reading Insight. Wishing you all the best.

  2. What are the percentages of women who have a recurrence after five years of tamoxifen and after ten years of tamoxifen?

    • Dear Pam –

      Thank you for your question and for reading Insight. Recurrence risk depends on the initial stage of the breast tumor. For women with stage I breast cancers, the average recurrence risk in years 5-10 is about 5 percent. For women with stage II or III breast cancers, the average recurrence risk in years 5-10 is about 10-15 percent.

      I hope this is helpful. Wishing you all the best!

  3. I was asking about those women who take tamoxifen. Does taking it for ten years offer a huge difference over taking it for five years? What are the numbers?

  4. If a patient with stage 1 HR+ breast cancer finished the 5 years of Aromasin 5 years ago, is it recommended that she go back on it now for another 5 years?

    • Dear Susan –

      Thank you for your comment and for reading Insight. Unfortunately, we cannot give out medical advice on this blog, or over email. We recommend bringing your question to an oncologist or care team. If you are looking for more information on breast cancer treatment, research and clinical trials, you can visit our Breast Oncology Program website.

      Wishing you all the best!

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