Back August 15, 2017

Restarting Anti-Estrogen Therapy for Breast Cancer

anti-estrogen therapy

Anti-estrogen therapy is an important part of the treatment for patients with early stage estrogen-receptor-positive breast cancer. For many women, the benefits of long term anti-estrogen therapies including aromatase inhibitors (AI) or tamoxifen include longer disease-free survival and lower rates of breast cancer forming in the other breast.1 These treatments can greatly improve a patient’s odds of beating cancer, but they also can come with difficult side effects and toxicities. If you are or have received anti-estrogen therapy you may have experienced bone and joint pain, bone thinning, hot flashes, mood swing, loss of libido, headaches, fatigue, vomiting, or other known side effects.2 Women stop their anti-estrogen therapy for many reasons. Some women stop before the 5-year mark due to side effects, others stop at year 5 either after a discussion with their physician or their own personal decision not to continue, and some women on extended anti-estrogen therapy will stop before the 10 year mark due to side effects, worry about the risk, cost, or many other issues. Many women find that the side effects of these medications have a significant impact on their quality of life, making them not feel like themselves, and causing some women to stop their anti-estrogen therapy. In fact, it was found that over half of breast cancer patients stop, temporarily or permanently, their anti-estrogen therapy.3

The Risk-Benefit Ratio and You

When doctors are deciding the best treatments for their patients they often think in terms of the risk- benefit ratio. This simply means they consider the likelihood of positive benefit of a certain course of treatment, and weigh it against the potential negative effects of that treatment. When a doctor is considering extending anti-estrogen therapy for a woman with early stage ER+ breast cancer beyond year 5, it is particularly important for the doctor to keep both sides in mind. However, how a patient feels on her anti-estrogen therapy may impact her view of her personal risk-benefit. Sometimes this leads to some women stopping their therapy despite their doctor’s recommendation to continue.

Why Women Stop Their Anti-Estrogen Therapy

Studies have shown that a common set of problems are often the reason that women may decide upon themselves to discontinue anti-estrogen therapy.3 The common problems associated with stopping anti-estrogen therapy include side effects, worry over risk of medication, general dislike of medication, and uncertainty on whether the medication is helping.4 These common issues lead to poor adherence to anti-estrogen therapy, further increasing their risk of recurrence.

The positive health outcomes of anti-estrogen therapies like aromatase inhibitors or tamoxifen that have been observed in groups of patients, may also come with significant side effects in certain individuals. For example, studies of tamoxifen have shown that 5 years of treatment for patients with ER-positive breast cancer significantly reduced the annual death rate and risk of the cancer coming back.5 However, it has been well documented that tamoxifen treatment is associated with increased occurrence of vaginal bleeding, uterine polyps (mass within inner lining of uterus) and ovarian cysts.1 Aromatase inhibitors have been shown to reduce the recurrence of breast cancer and improve the disease-free survival rate.6 But again, these positive results are met with serious side effects like increased odds of developing cardiovascular disease and bone fractures.10 These side effects can lead women to stop their treatment, claiming the side effects are too much to handle. It is important that your doctor consider both the benefits and risk of treatment in order to provide you with care that can keep you healthy and help you maintain a high quality of life.

Additionally, recent studies have shown the benefits of extending AI therapy from the typical five years to ten years. One study showed patients who received 10 year of AI treatment had significantly higher rates of disease-free survival and lower occurrence of breast cancer on the opposite breast.7 With the many side effects of AI therapy, a patient may find herself asking “Can I really do this for another 5 years?” Once these questions arise, we begin to see an increasing number of women abandon their treatments, as discussed earlier. In fact, in these extended anti-estrogen therapy trials it was found that close to 40% of patients prematurely discontinued their therapy.4,8

What tools are available to evaluate your personal risk-benefit ratio?

You’ve made a list of pros and cons with your doctor; are you ready to make a decision? Everybody knows that medicines come with side effects, but it is hard to determine whether a treatment is right for you. Breast cancer can be a time of many uncertainties from diagnosis throughout treatment and dealing with anti-estrogen therapy can add even more uncertainty. Patients at the beginning of diagnosis struggling with tolerating anti-estrogen therapy are often left wondering how long they will need to take these pills. Patients approaching the 5-year anniversary of diagnosis want to know if they should continue treatment beyond 5 years. Finally, even patients 5-8 years post diagnosis have questions like “Do I have to be on for the full 10 years?”

What can you do to improve your bone health naturally? It’s easier than you think!

A tool doctors use to answer questions like these for their patients is a biomarker test to better understand your tumor at the biological level, which may hold hidden information to best personalize your treatment. A test called the Breast Cancer Index, or BCI, actually gives your doctor a look within the biology of your tumor, identifying genes that can tell him or her about your likelihood to benefit from extended anti-estrogen therapy and your risk of recurrence in the future. The physicians, upon incorporation of BCI results, changed their recommendations for 30% of patients and 61% of patients changed their treatment preference.9 Additionally, patients experienced significantly less anxiety and internal conflict associated with the decision after discussing the BCI test results with their physician.9

If your Breast Cancer Index results indicate you are at a low risk of late distant recurrence and have a low likelihood of benefit from more anti-estrogen therapy, your physician may provide an end goal of 5 years to work towards. You can take your medication and make sure to comply, knowing that the end of your treatment is near. If you are at a high risk of recurrence and a high likelihood of benefit, many women adopt a new, more aggressive attitude toward their breast cancer treatment. In fact, 82% of patients reported that knowing the BCI results would make them more likely to be compliant with extended therapy.9,11 Women see this as an opportunity to beat breast cancer. They know from their test results that to get better and beat this disease, they need to be following their treatments. Additionally, knowing that they have a high likelihood of benefit from continuing therapy allows women to incorporate new strategies for fighting the potential side effects of extended anti-estrogen therapy.

If you are part of the over 50% of women that have stopped their anti-estrogen therapy, do you really need to restart?

If you have recently stopped your adjuvant anti-estrogen therapy it is important you talk to your doctor about whether restarting is right for you. A study from April of 2017 showed the benefits of restarting therapy after stopping temporarily. This study published in Journal of the National Cancer Institute found common factors like, younger age (3 In these women that were able to restart, the study found that they had a significant increase in disease-free survival rate.3

If you are a woman with early stage ER+ breast cancer who has stopped taking anti-estrogen treatment, talk to your doctor about some of the issues that prevented you from continuing, and see if restarting may help you lower your risk of breast cancer recurrence.



  4. Mamounas EP et al. San Antonio Breast Cancer Symposium, 2016
  5. Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), Effects of chemotherapy and hormonal therapy for early breast cancer on recurrence and 15-year survival: an overview of the
  6. Dowsett M, Cuzick J, Ingle J, et al. Meta-analysis of breast cancer outcomes in adjuvant trials of aromatase inhibitors versus tamoxifen, J Clin Oncol., 2010, vol. 28 3(pg. 509-518)
  8. Goss P. et al: NEJM 2016
  9. Sanft et al. San Antonio Breast Cancer Symposium, 2016
  11. Sanft T et al. ASCO Quality Care Symposium, 2017


NOTE: This material was created by or on behalf of Biotheranostics, Inc. The content, products and services discussed in this material are offered to educate healthcare providers and/or consumers on molecular diagnostic testing performed by Biotheranostics, and should not be considered or used as a substitute for medical advice, diagnosis or treatment of specific medical conditions. To see BCI Intended Use & Limitations, please visit