Background: AET for postmenopausal women with HR+ early BC has until recently been limited to 5 yrs of tamoxifen, an aromatase inhibitor or a sequential combination of these. However, after 5 yrs of AET, BC events continue to occur at a high rate (2% per yr) for at least another 10 yrs. The LATER trial was designed to compare 5 yrs of Let 2.5mg daily as late reintroduction of AET to Obs ( = usual care) in postmenopausal women after ≥ 4 yrs of AET. Methods: LATER was a prospective open label randomized trial for postmenopausal women who were BC free and had completed ≥ 4 yrs of AET for HR+ early BC more than 1 yr prior to study entry. The primary outcome was the rate of invasive BC events (defined as new invasive primary, local, regional or distant recurrence or contralateral BC) for Let arm compared to Obs. Secondary outcomes included disease-free survival (DFS), overall survival (OS) and toxicity. To reject the null hypothesis in favor of a 60% reduction in the primary outcome with β = 0.10 and 2α = 0.05, 1700 patients were required. In Oct 2014 the independent data and safety monitoring committee recommended to cease trial follow up and to release the data for analysis due to a low event rate. Results: Between May 2007 and March 2012, 360 patients were randomized (181 Let; 179 Obs), after which enrolment ceased due to a low accrual rate. Patients completed prior AET a median of 2.5 yrs before randomization. N+ 33.9%, N- 60.0%, unknown 6.1%. Prior AET was aromatase inhibitor only in 11.1%, SERM in 50.6% and a sequential combination in 38.3%. In the ITT population, at a median 3.0 yrs follow-up, 1.1% of patients in the Let arm had experienced an invasive BC event vs 8.4% in the Obs arm (difference 7.3%, 95% CI 2.9-11.6, p = 0.001, conditional binomial exact test). DFS events occurred in 6.1% vs 11.7% (p = 0.06) and death in 1.7% vs 2.2% (p = 0.70) in the Let and Obs arms respectively. Conclusion: In postmenopausal women who had completed ≥ 4 yrs of AET for HR+ early BC, Let significantly reduced the incidence of late invasive BC events. Clinical trial information ACTRN 012607000137493. Clinical trial information: 01260700013749.