The authors of this paper present the 5-year outcome analysis of Austrian Breast and Colorectal Cancer Study Group 8 (ABCSG-8). The ABCSG-8 study ABCSG-8 is a prospective, multicentre randomised, open-label study comparing 5 years of tamoxifen (TAM) treatment with 2 years of TAM followed by 3 years of anastrozole (ANA). Study participants were in the low- to moderate-risk group of endocrine receptor positive, postmenopausal patients with breast cancer not receiving any other systemic therapy. Random assignment occurred immediately after surgery, and no (neo) adjuvant chemotherapy was allowed. Both groups of patients were treated with an initial 2 years of tamoxifen (TAM) and sequenced to anastrozole (ANA) versus TAM for an additional 3 years.

The primary end point measure for this analysis was recurrence-free survival (RFS) defined as time from random assignment to the earliest occurrence of local or distant recurrence or death as a result of any cause. Exploratory survival end points and toxicity were also investigated. Analyses were carried out on an intention to treat and censored basis. Information from 3,714 patients, including 17,563 woman-years, with a median of 60 months of follow-up was available for the current analysis. The following results are reported:

• Median age was 63.8 years, 75% were node negative, and 75% had T1 tumors.

• Sequencing of ANA after identical 2-year treatment with TAM in both arms did not result in a statistically significant improvement of RFS (hazard ratio [HR], 0.80; 95% CI, 0.63 to 1.01; P = .06).

• Exploratory analyses of distant relapse-free survival indicated a 22% improvement (HR, 0.78; 95% CI, 0.60 to 1.00).

• On-treatment adverse events and serious adverse events were consistent with known toxicity profiles of ANA and TAM treatment.

The authors conclude, “Despite a low overall rate of recurrence in a population with breast cancer at limited risk of relapse, the a priori sequence strategy of 2 years of TAM followed by 3 years of ANA led to small outcome and toxicity benefits.”