Breast Cancer Recurrence Risk Drops Significantly if Hormone Therapy Extended Beyond Five Years

People with oestrogen receptor-positive breast cancer who extend their hormone-blocking therapy treatment beyond the standard five years by switching to, or continuing treatment with an aromatase inhibitor drug, could further reduce the risk of their cancer returning. 

In August 2025, the international Early Breast Cancer Trialists’ Collaborative group published a meta-analysis in the Lancet, in which they combined and analysed the data from 12 randomised controlled trials involving more than 22,000 postmenopausal women with hormone-sensitive early stage breast cancer. 

All women had already had at least five years of hormone-blocking therapy with either tamoxifen or another class of drugs called aromatase inhibitors, and were cancer-free at the entry to the study. The meta-analysis then looked at what happened to women who continued their treatment beyond five years compared to those who didn’t. Researchers saw a significant benefit from continuing treatment for up to an extra five years, and particularly if that continued treatment was with an aromatase inhibitor. 

The greatest benefits were seen in women who had previously received five years of tamoxifen therapy then switched to an aromatase inhibitor for a further one to four years of treatment. Their relative risk of recurrence in those one to four years was almost halved compared to the risk in women not taking any continued hormone blocking therapy. 

In women who were originally treated with aromatase inhibitors, a further five years of the same treatment reduced their risk of recurrence by 26% compared to those who didn’t continue treatment. Even taking the additional aromatase inhibitor therapy for two to three years reduced the risk of recurrence. 

Medical oncologist Dr Nicholas Zdenkowski, Chair of the Breast Cancer Trials Scientific Advisory Committee, said it was important to show a benefit from extended therapy, to enable decisions in the clinic at the five-year mark to allow clinicians and patients to understand options to minimise recurrence risk.  

There needs to be a shared decision-making approach to weigh up the pros and cons, he said, because of the side effects that may be experienced with aromatase inhibitor treatment, which include hot flushes, insomnia, vaginal dryness, fatigue, bone density loss and arthritis. 

“We need to make sure that if we’re going to offer these patients treatment for longer than five years, that we’re benefiting them in doing so,” Dr Zdenkowski said. “This shows that an additional five years beyond their standard five years achieves a statistically significant improvement in disease-free survival, irrespective of their baseline risk.” 

The benefit of extended treatment was even greater among women with a higher risk of recurrence at the start of the study because their cancer had already spread to the nearby lymph nodes. 

“If they’ve got higher risk node-positive disease, and there’s more a 5% absolute difference in benefit, then they may be more motivated to continue despite the side effects,” Dr Zdenkowski said.  

Publication: 

Early Breast Cancer Trialists Collaborative Group (EBCTCG). Extending the duration of endocrine treatment for early breast cancer: patient-level meta-analysis of 12 randomised trials of aromatase inhibitors in 22031 postmenopausal women already treated with at least 5 years of endocrine therapy. The Lancet. 2025; 406 (10503) 603-614 epub 7 August 2025