Abstract S1-03: First results from the multicenter phase III DATA study comparing 3 versus 6 years of anastrozole after 2-3 years of tamoxifen in postmenopausal women with hormone receptor-positive early breast cancer
Authors: Tjan-Heijnen VC , Van Hellemond IE , Peer PG , Swinkels AC , Smorenburg CH , Van der Sangen M , Kroep JR , De Graaf H , Honkoop AH , Erdkamp F , Van den Berkmortel FW , Kitzen JJ , De Boer M , De Roos WK , Linn SC , Imholz AL , Seynaeve C 
Published: March 2017

Background. Even in view of the recent findings of the MA.17R trial, the impact of prolonged aromatase inhibitor (AI) therapy after prior tamoxifen in hormone receptor-positive early breast cancer remains insufficiently clear.

Methods. In this open-label phase III study, we randomly assigned 1912 postmenopausal women with hormone receptor-positive breast cancer after 2-3 years of adjuvant tamoxifen to either 3 or 6 years of anastrozole therapy. The primary endpoint was the adapted disease-free survival (ADFS). This was defined as the DFS beyond 3 years after randomization to AI therapy because initially all patients received the same AI therapy for 3 years. ADFS events included (non-) invasive breast cancer recurrences (local, regional, distant), second primary (non-) invasive (breast) cancers, and death of any cause. The study was designed to detect an increase of the ADFS in the 6-year versus the 3-year anastrozole group corresponding with a hazard ratio (HR) of 0.60. The HRs and the corresponding 95% confidence intervals (CIs) were estimated with stratified Cox proportional-hazard models according to intention-to-treat.

Results. Patients were randomized from July 2006 till August 2009. Three years after randomization 1663 patients had no DFS events, with an equal distribution between the treatment arms. The patient and tumor characteristics were well balanced. The median age at randomization was 57 years (P5 = 45 years, P95 = 76 years), the median primary tumor size was 21 mm (P5 = 10 mm, P95 = 50 mm), 67% of the patients had node-positive disease, and in 2% the tumor was HER2-positive (14% unknown); 64% of the patients had received adjuvant chemotherapy and &lt;1% adjuvant trastuzumab. The median adapted follow-up was 4.1 years (P5 = 2.9 years, P95 = 5.8 years). No unexpected safety issues were seen. The 5-year ADFS was 79% in the 3-year and 83% in the 6-year anastrozole treatment group, yielding a HR for ADFS-event of 0.78 (95% CI 0.61 to 1.00; p = 0.0528). In patients with node-positive disease (N = 1117), the HR for ADFS-event was 0.71 (95% CI 0.53 to 0.96; p=0.0232), in N0 disease (N=546) 1.01 (95% CI 0.62 to 1.63; p=0.9817) and in patients with both ER and PR positive breast cancer (N = 1264) 0.68 (95% CI 0.51 to 0.90; p=0.0072). The 5-year adapted overall survival was not different between the treatment groups.

Conclusion. These findings do not yet support the use of extended adjuvant AI prescription after 5 years of sequential endocrine therapy for postmenopausal patients with hormone receptor-positive breast cancer, but suggest benefit for a selected group of patients. Continued follow-up is needed to assess long-term efficacy and safety.

Funding. Funded by AstraZeneca NL, ClinicalTrials.gov number, NCT00301457.

Citation Format: Tjan-Heijnen VC, Van Hellemond IE, Peer PG, Swinkels AC, Smorenburg CH, Van der Sangen M, Kroep JR, De Graaf H, Honkoop AH, Erdkamp F, Van den Berkmortel FW, Kitzen JJ, De Boer M, De Roos WK, Linn SC, Imholz AL, Seynaeve C. First results from the multicenter phase III DATA study comparing 3 versus 6 years of anastrozole after 2-3 years of tamoxifen in postmenopausal women with hormone receptor-positive early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S1-03.