GEICAM/2006-10 compared anastrozole (A) versus fulvestrant plus anastrozole (A + F) to test the hypothesis of whether a complete oestrogen blockade is superior to aromatase inhibitors alone in breast cancer patients receiving hormone adjuvant therapy.

Multicenter, open label, phase III study. HR+/HER2- EBC postmenopausal patients were randomized 1:1 to adjuvant A (5 years [year]) or A + F (A plus F 250 mg/4 weeks for 3 year followed by 2 year of A). Stratification factors: prior chemotherapy (yes/no); number of positive lymph nodes (0/1-3/≥ 4); HR status (both positive/one positive) and site.

disease-free survival (DFS). Planned sample size: 2852 patients.

The study has an early stop due to the financer decision with 870 patients (437 randomized to A and 433 to A + F). Patient characteristics were well balanced. After a median follow-up of 6.24y and 111 DFS events (62 in A and 49 in A + F) the Hazard Ratio for DFS (combination vs. anastrozole) was 0.84 (95% CI 0.58-1.22; p = 0.352). The proportion of patients disease-free in arms A and A + F at 5 year and 7 year were 90.8% versus 91% and 83.6% versus 86.7%, respectively. Most relevant G2-4 toxicities (≥ 5% in either arm) with A versus A + F were joint pain (14.7%; 13.7%), fatigue (2.5%; 7.2%), bone pain (3%; 6.5%), hot flushes (3.5%; 5%) and muscle pain (2.8%; 5.1%).

The GEICAM/2006-10 study did not show a statistically significant increase in DFS by adding adjuvant F to A, though no firm conclusions can be drawn because of the limited sample size due to the early stop of the trial. ClinicalTrials.gov: NCT00543127.