Extending adjuvant anastrozole therapy from 3 to 6 years after up to 3 years of tamoxifen does not improve breast cancer survival outcomes, according to first results from the phase 3 DATA trial (ClinicalTrials.gov Identifier: NCT00301457) presented at the 2016 San Antonio Breast Cancer Symposium.

“The findings of the DATA study do not support extended adjuvant AI use after 5 years of sequential endocrine therapy for all postmenopausal hormone receptor-positive breast cancer patients,” reported Vivianne Tjan-Heijnen, MD, PhD, of Maastricht University Medical Center in the Netherlands.

The study suggests a possible benefit for selected patients who have both estrogen receptor (ER) and progesterone receptor (PR) positive disease, HER2-negative disease, large tumor loads, and prior chemotherapy, she said.

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Extended AI therapy is, however, associated with increased bone and muscle toxicity.

Upfront or sequential aromatase inhibitors (AIs) after 2 to 3 years of tamoxifen for treatment duration of 5 years has been shown to reduce the risk of tumor recurrence compared to 5 years of adjuvant tamoxifen, noted Dr Tjan-Heijnen.

The DATA study assessed survival benefits of extended AI for patients treated with tamoxifen and then AI. Researchers enrolled 1860 eligible postmenopausal women treated breast cancer who had no metastases, no signs of tumor recurrence, and who had completed 2 to 3 years of adjuvant tamoxifen.

Participants were stratified by nodal status, ER/PR status, HER2 status, and duration of tamoxifen treatment. The patients were then randomized to receive either 3 years (929 patients) or 6 years (931 patients) of anastrozole.

There was a trend toward numerically superior adapted disease-free survival (aDFS) among patients in the 6-year group, but this difference did not reach statistical significance (5-year aDFS: 83% vs 79.4%; hazard ratio [HR], 0.79; P = 0.07).

Nor did adapted overall survival (aOS) differ between the 2 groups (5-year aOS: 90.8% vs 90.4%; P = 0.60).

Subsequent subgroup analysis suggested an aDFS benefit for extended therapy among node-positive, ER+, PR+, HER2-negative patients (5-year aDFS: 86% vs 76%; HR, 0.58; P = 0.01).

RELATED: No Breast Cancer Survival Benefit for Extending Adjuvant Letrozole Therapy to 5 Years

Predefined adverse events included arthralgia/myalgia, bone fractures, osteopenia/osteoporosis, and cardiovascular adverse events, including arrhythmia.

“We will perform a follow-up analysis when all patients have reached a minimum adapted follow-up of 9 years,” Dr Tjan-Heijnen said.


  1. Tjan-Heijnen VC, Van Hellemond IE, Peer PG, et al. S1-03: First results from the multicenter phase III DATA study comparing 3 versus 6 years of anastrazole after 2-3 years of tamoxifen in postmenopausal women with hormone receptor-positive early breast cancer. Paper presented at: 39th San Antonio Breast Cancer Symposium; Dec 2016; San Antonio, TX.