What My Patients Are Asking: Should I Take Tamoxifen for 10 Years Instead of 5?

By on June 26th, 2013 Categories: Research News

Two big studies that came out in the last 6 months – the ATLAS trial and the aTTOM trial – have found that taking tamoxifen for 10 years instead of 5 years offers more benefits, including:

  • reducing the amount of recurrence
  • reducing the number of deaths from breast cancer
  • improving overall survival

Before these studies came out, most premenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer took 5 years of tamoxifen therapy to lower the risk of recurrence. Premenopausal women take tamoxifen and postmenopausal women have a choice between tamoxifen or an aromatase inhibitor such as Arimidex (chemical name: anastrozole), Aromasin (chemical name: exemestane), or Femara (chemical name: letrozole).

Now, the ATLAS and aTTOM results are starting to change treatment standards for early-stage, hormone-receptor-positive breast cancer.

Being cancer-free 5 years after diagnosis is a big milestone for cancer patients. It’s a big milestone for doctors, too. That’s when we start using the word “cure.” That’s partially why earlier studies on tamoxifen used 5 years as a treatment time period. Still, we know that women can have breast cancer recurrences 7 years, 8 years, 10 years, or more after diagnosis. That’s one reason doctors wanted to see if taking tamoxifen for a longer time would offer more benefits.

But should all women diagnosed with early-stage, hormone-receptor-positive breast cancer take tamoxifen for 10 years?

In my opinion, no. While many, many women will benefit from 10 years of tamoxifen, there is a group that would do better with another type of treatment.

First, let’s talk about who probably should take tamoxifen for 10 years: Younger women diagnosed with early-stage, hormone-receptor-positive breast cancer who won’t start menopause for at least 10 years when they begin taking tamoxifen. The results from the studies apply mainly to this group of women.

Tamoxifen is the preferred hormonal therapy for younger women. Tamoxifen blocks the effects of estrogen in the breast tissue by sitting in the estrogen receptors in breast cells. If tamoxifen is in the estrogen receptor, there is no room for estrogen and it can’t attach to the cell. If estrogen isn’t attached to a breast cancer cell, the cell doesn’t receive estrogen’s signals to grow and multiply.

Aromatase inhibitors, on the other hand, stop the production of estrogen in the body by blocking the enzyme aromatase, which turns androgen hormones into small amounts of estrogen. Aromatase inhibitors can’t stop the ovaries from making estrogen, so they only work in postmenopausal women.

While most younger women will get more benefits from 10 years of tamoxifen versus 5, it’s important to know that tamoxifen can cause side effects, some of them serious. In fact, side effects such as hot flashes and night sweats are why some women stop taking tamoxifen before they’ve finished the first 5 years of the medicine. We know that tamoxifen also can increase the risk of endometrial cancer. The ATLAS study found the risk of endometrial cancer to be 1.6% after 5 years of tamoxifen; 10 years of tamoxifen increased that risk to 3.1%. So younger women at high risk for endometrial cancer will need to weigh the risks and benefits of taking tamoxifen for another 5 years. In some cases it may mean that these women take tamoxifen for only 5 years.

It is important to note, however, that a woman is 10 times more likely to have her life saved by another 5 years of tamoxifen than she is to get endometrial cancer, so the benefits usually far outweigh the risks. The benefit of tamoxifen continues even after the 10 years is up.

Older women who start menopause during the first 5 years of tamoxifen are better off taking an aromatase inhibitor for another 5 years, for a total of up to 10 years of hormonal therapy.

So when my patients ask me if they should take tamoxifen for another 5 years, I first ask them whether they’ve gone through menopause and then we discuss her risk for endometrial cancer and whether it’s higher than average. If the answers to those questions are “no,” then I recommend another 5 years of tamoxifen. Alternatively, she could opt to have her ovaries removed and get a similar effect.

I also recommend that any woman who’s been diagnosed with breast cancer have at least one visit per year with her oncologist, whether she’s still taking any sort of breast cancer medicine or not. Because we know breast cancer can come back many years after the initial diagnosis, it’s important for the oncologist to check your general health as well as do any screenings that are needed in your unique situation. If you’re going to be taking tamoxifen or an aromatase inhibitor for another 5 years, your doctor also will want to know about any side effects you’re having and steps you’re taking, if any, to ease those side effects.

I’ve told you my thoughts, now I’m curious about yours. How many of you have talked to your doctors about taking tamoxifen (or an aromatase inhibitor) for another 5 years? How do you feel about it?

Editor’s Note: All information is intended for your general knowledge only and is not a substitute for medical advice or medical treatment. The information provided on this site is designed to support, not replace, the relationship that exists between a patient/site visitor and her/his existing physician. Please consult your healthcare professional on any question you may have. You should never disregard medical advice or delay in seeking medical advice because of something you read here.

Brian S. Wojciechowski, M.D. joined the Breastcancer.org team as medical adviser in July 2012. He specializes in the care of patients with cancer and practices medical oncology in Delaware County, Pennsylvania at Riddle, Taylor, and Crozer Hospitals. A proud native of South Philadelphia, he trained at Temple University School of Medicine and Lankenau Medical Center. His research has been presented at the San Antonio Breast Cancer Symposium, the world's largest scientific meeting on breast cancer. Dr. Wojciechowski is a sought-after speaker on the topics of medical ethics and the biology of cancer. Beyond medicine, he is devoted to his faith, his family, and his guitar. He sees cancer as a scientifically complex disease with unique psychological, social, and spiritual dimensions, a perspective he takes into relationships with patients.


  1. Brian Wojciechowski, M.D.
  2. Brian Wojciechowski, M.D.

Leave a Comment

To keep our Community safe, you must register to start a topic, post a reply, or use the Chat Rooms. If you are an existing member of our Discussion Boards, you can log in to access your account. Please review our Privacy Statement before registering.

Register now or log in to your account.

Back to top

Breastcancer.org is a non-profit organization dedicated to providing information and community to those touched by this disease. Learn more about our commitment to providing complete, accurate, and private breast cancer information.

Breastcancer.org 120 East Lancaster Avenue, Suite 201 Ardmore, PA 19003

© 2021 Breastcancer.org - All rights reserved.