extended therapy (total duration of endocrine therapy of more than 5 years) with an aromatase inhibitors or tamoxifen in breast cancer

Last edited 03/2021 and last reviewed 03/2023

Extended endocrine therapy

an aromatase inhibitor

  • extended therapy (total duration of endocrine therapy of more than 5 years) with an aromatase inhibitor should be offered for postmenopausal women with ER (oEstrogen receptor)-positive invasive breast cancer who are at medium or high risk of disease recurrence and who have been taking tamoxifen for 2 to 5 years
  • extended therapy (total duration of endocrine therapy of more than 5 years) with an aromatase inhibitor should be considered for postmenopausal women with ER-positive invasive breast cancer who are at low risk of disease recurrence and who have been taking tamoxifen for 2 to 5 years

tamoxifen

  • consider extending the duration of tamoxifen therapy for longer than 5 years for both premenopausal and postmenopausal women with ER-positive invasive breast cancer. [2018]

Effects of extended endocrine therapy

  Extended tamoxifen therapy (after an initial 5 years of tamoxifen therapy) Extended endocrine therapy with an aromatase inhibitor (after 5 years of tamoxifen therapy)
Definition Continuing to take tamoxifen after 5 years of tamoxifen therapy. Switching to an aromatase inhibitor after 5 years of tamoxifen therapy
Who can take this therapy Premenopausal or postmenopausal women with ER-positive invasive breast cancer. Postmenopausal women with ER-positive invasive breast cancer.

Effect on breast cancer recurrence

NOTE: The benefit for an individual person will depend on the risk of their cancer returning. For people with a low risk of recurrence, the benefits may not outweigh the risks or side effects.

Medium or high risk may include people who have lymph node-positive breast cancer, with tumours that are T2 or greater and higher grade. Low risk may include people with lymph node-negative breast cancer, with smaller or lower-grade tumours.

 Lower rates of breast cancer recurrence compared with 5 years of tamoxifen therapy

Lower rates of breast cancer recurrence compared with 5 years of tamoxifen therapy. I

n postmenopausal women, switching to an aromatase inhibitor may be more effective at reducing recurrence than continuing with tamoxifen

Side effects

NOTE: These are common side effects experienced during additional years taking endocrine therapy. Most effects are reversible when tablets are stopped

Side effects of endocrine therapy will continue for additional years (for example, menopausal symptoms such as hot flushes).

With extended use of tamoxifen: increased risk of thrombosis and endometrial cancer, and possibly bone density loss in premenopausal women.

Side effects of endocrine therapy will continue for additional years (for example, menopausal symptoms such as hot flushes).

With extended use of aromatase inhibitors: bone density loss, and joint and muscle pain.
Fertility and family planning Effects on fertility and family planning will continue for additional years as women should not become pregnant while taking tamoxifen, or within 2 months of stopping, because it may have adverse effects on the baby. Not applicable as postmenopausal women only.

The aTTom study (2)

  • confirms that, in ER+ disease, continuing tamoxifen to year 10 rather than just to year 5 produces further reductions in recurrence, from year 7 onward, and breast cancer mortality after year 10
  • taken together with the reduction in breast cancer deaths seen in trials of 5 years of tamoxifen vs none, these results indicate that 10 years of adjuvant tamoxifen, compared to no tamoxifen, reduces breast cancer mortality by about one third in the first 10 years following diagnosis and by a half subsequently

Reference:

Related pages:

breast cancer

tamoxifen

aromatase inhibitors