Five or more years of adjuvant endocrine therapy in breast cancer: a meta-analysis of published randomised trials

Five years of adjuvant hormonal therapy is the standard of care in early breast cancer (BC) expressing oestrogen receptors (ER+). Prolonged duration of adjuvant endocrine therapy is implemented to prevent recurrence and death; in particular, its carryover effect may prevent very late events. This meta-analysis compares the efficacy of 5 years of hormonal therapy alone with that of additional years of hormonal therapy, in patients with early BC. Randomised trials comparing 5 years versus more than 5 years of hormonal therapy in BC were identified by electronic searches of PubMed, EMBASE, ISI Web of Science and the Cochrane Central Register of Controlled Trials. Meta-analysis was performed using the fixed- or random-effects models. The primary endpoints were overall survival (OS), BC-specific survival (BCSS) and relapse-free survival (RFS) reported as odds ratios (ORs) and 95 % confidence interval (CI). Eight trials, including 29,138 patients, were identified. Overall, in ER+ BCs, extended endocrine therapy beyond 5 years of tamoxifen significantly improved OS (OR, 0.89; 95 % CI 0.80-0.99; P = 0.03), BCSS (OR, 0.78; 95 % CI 0.69-0.9; P = 0.0003) and RFS (OR 0.72; 95 % CI 0.56-0.92; P = 0.01) compared with 5 years of hormonal therapy alone. Loco-regional and distant relapses were reduced by 36 and 13 %, respectively. Compared with 5 years of tamoxifen, additional adjuvant endocrine therapy reduced risk of death and relapse of ER+ BC by similar to 10 and 30 %, respectively. This strategy should be considered in patients free of disease after 5 years of hormonal therapy.