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18-12-2017 | Hormone-receptor positive breast cancer | News

Two-year adjuvant AI extension may be enough in postmenopausal breast cancer

medwireNews: Among postmenopausal women with hormone receptor-positive breast cancer receiving standard adjuvant aromatase inhibitor (AI) therapy, extending treatment by 2 years is associated with similar outcomes to a 5-year extension, but with fewer side effects, an Austrian trial suggests.

The results of the phase III ABCSG-16 study were presented at the 2017 San Antonio Breast Cancer Symposium in Texas, USA, by Michael Gnant, from the Medical University of Vienna.

He told the conference delegates that they recruited 3469 women with stage I–III disease who were recurrence-free after 5 years of adjuvant treatment with tamoxifen, an AI, or tamoxifen followed by an AI. The participants were randomly assigned to receive either a further 2 or 5 years of anastrozole 1 mg/day and followed up for a median of 106.2 months.

The primary endpoint of disease-free survival did not differ significantly between groups, with 10-year rates of 71.1% and 70.3% in the 2- and 5-year groups, respectively.

Overall survival was also comparable for the 2- and 5-year arms, with a respective 85.3% and 84.9% of patients alive at 10 years, and the time to secondary carcinoma and time to contralateral breast cancer were similar as well, Gnant reported.

But the 2-year regimen appeared to have a better toxicity profile, in that bone fractures occurred less frequently in the 2-year extended anastrozole group, at 4.7% compared with 6.3% in the 5-year group, although the difference did not reach significance.

Around 80% of women in each group were adherent to the treatment at the 2-year mark, but the adherence rate in the 5-year arm declined steadily after that, dropping to around 65% by 5 years.

Gnant summarized that there seems to be “no benefit of continuing/escalating endocrine treatment beyond 7 years,” and in fact, “[e]xtension of anastrozole treatment [for] 5 additional years leads to increased side effects including fractures, and should be avoided.”

He noted, however, that “[i]n the future, translational research may identify molecular characteristics that indicate benefit of prolonged extended therapy.”

By Shreeya Nanda

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