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Continuing treatment with aromatase inhibitors (a type of hormone therapy) for another five years further reduces the risk of developing secondary breast cancer by over a quarter for certain women. These results from the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), based at Oxford Population Health, are published in The Lancet.

A 3D medical illustration of breast cancer

About three quarters of postmenopausal women with operable breast cancer have hormone-sensitive disease. For these women, five years of endocrine (hormone) treatment after surgery, either with tamoxifen or aromatase inhibitor tablets, reduces the risk of dying from breast cancer by about a third, with benefits continuing well beyond the end of treatment. However, despite this, there remains a substantial and constant risk of late breast cancer recurrence and death.

Addressing variation in clinical practice

Current clinical practice varies, with some women recommended five years of treatment in total, some seven years, and some longer. Individual trials where endocrine treatments have been continued for two to five years after an initial five years of treatment have shown promising but inconclusive results on the benefits of continuing treatment for longer.

Researchers from the EBCTCG, which is funded by Cancer Research UK and the Breast Cancer Research Foundation (BCRF), gathered data from over 22,000 women in all 12 randomised clinical trials that compared further endocrine therapy using an aromatase inhibitor with no further treatment to assess the benefits and risks of additional treatment.

Key results:

  • Allocation to five more years of aromatase inhibitor therapy (AIT) reduces the risk of secondary breast cancer by over one-quarter (27%) compared to stopping therapy in postmenopausal women with oestrogen receptor positive (hormone-sensitive) early breast cancer who have completed five years of hormone treatment that included AIT;
  • This proportional benefit was consistent among all women, but absolute benefits were greater in women who were at higher risk of secondary breast cancer, particularly those whose initial cancer had spread to their lymph nodes;
  • Over one-third of women stopped taking their treatment, so the benefits may be even larger in women who are able to adhere to treatment;
  • The follow-up period in the trials was too short to determine whether this improvement would translate into reducing death from breast cancer;
  • There was no evidence of an increased risk of death from other non-breast cancer causes, including heart disease. However, women allocated to longer treatment experienced a small increase in bone fracture incidence of 1.2%.

 

Read the full story on the Nuffield Department of Population Health website.