The open-label, multicenter phase 3 DATA study was designed to evaluate the benefit of extended aromatase inhibitor use beyond 5 years in women with hormone receptor–positive, early breast cancer who were treated with sequential endocrine therapy. Researchers randomized patients—who had received 2 to 3 years of adjuvant tamoxifen and who had no signs of disease recurrence—in a 1:1 ratio to extended treatment with either 3 or 6 years of anastrozole. Thus, these patients received 5 to 6 years or 8 to 9 years of endocrine therapy in total. The primary end point of the study was adapted disease-free survival (DFS), defined as DFS beyond 3 years after randomization. Secondary end points included adapted overall survival (OS) beyond 3 years after randomization, incidence of secondary breast cancer, and adverse events.
A total of 1860 patients were enrolled in the trial. Recently, Tjan-Heijnen and colleagues reported the results of their primary end point analysis in 1660 patients who were disease-free 3 years after being randomized. Two-thirds of the patients had node-positive disease and three-quarters had estrogen receptor– and progesterone receptor–positive disease at the time of diagnosis.
The adapted DFS at 3 years was 90.7% in the 6-year anastrozole group versus 88.9% in the 3-year anastrozole group; the adapted DFS at 5 years was 83.1% versus 79.4%, respectively (P = .066).
A post-hoc analysis showed that patients with estrogen receptor– and progesterone receptor–positive expression and node-positive disease demonstrated improved 5-year adapted DFS of 84.4% with 6 years of anastrozole treatment (irrespective of chemotherapy use) versus 76.2% in the 3-year group (P = .0075).
The difference in adapted OS was not statistically significant with 6 years of anastrozole treatment (90.8%) versus 3 years of anastrozole treatment (90.4%; P = .60).
In addition, when looking at the incidence of secondary breast cancer, the difference was numerically superior but did not reach statistical significance with 6 years of anastrozole treatment (1.5%) versus 3 years of anastrozole treatment (3.3%; P = .068).
In the 6-year anastrozole group, the occurrence of all-grade arthralgia or myalgia was 58% versus 53% in the 3-year anastrozole group, and osteopenia or osteoporosis was 21% versus 16% in the 3-year anastrozole group. However, grade 3/4 adverse events were similar between the 2 groups for arthralgia or myalgia and osteopenia or osteoporosis. No difference was found in the incidence of cardiovascular toxicity.
The authors concluded that extended use of anastrozole for 3 years beyond 5 years of sequential therapy did not significantly improve DFS or OS in the total study population. However, the findings from this trial suggest a benefit with extended anastrozole in patients with estrogen receptor– and progesterone receptor–positive disease.
Source: Tjan-Heijnen VCG, van Hellemond IEG, Peer PGM, et al; for the Dutch Breast Cancer Research Group (BOOG) for the DATA Investigators. Extended adjuvant aromatase inhibition after sequential endocrine therapy (DATA): a randomised, phase 3 trial. Lancet Oncol. 2017;18:1502-1511. Erratum in: Lancet Oncol. 2017;18:1502-1511.