Extended adjuvant endocrine therapy in early breast cancer: a meta-analysis of published randomized trials

Adjuvant endocrine therapy for 5 years is the standard adjuvant treatment for estrogen receptor-positive breast cancer while the benefits of extended adjuvant endocrine therapy (EAET) beyond 5 years are still controversial. That controversy prompted this meta-analysis to compare 5 years of adjuvant endocrine therapy only versus EAET. Eligible 11 randomized, controlled trials comprising 29,000 women were included. EAET showed no advantage in overall survival (OS) from all causes mortality (odds ratio [OR] = 0.98 (95% confidence interval [CI], 0.87-1.09); P = 0.67). On the other hand, compared with standard therapy, the pooled effects showed that EAET was associated with improvement in breast cancer-specific survival (OR = 0.87; 95% CI 0.79-0.96; P = 0.004), disease-free survival (DFS) (OR = 0.87; 95% CI 0.75-0.99; P = 0.002), disease recurrence (OR = 0.76; 95% CI 0.64-0.90; P = 0.001), and contralateral breast recurrence (OR = 0.74; 95% CI 0.59-0.93; P = 0.008). Improvement in DFS or disease recurrence was not shown in studies that compared 5 years of tamoxifen versus tamoxifen beyond 5 years. Subgroup analysis showed that EAET conferred more benefit for patients with positive lymph nodes. Rates of positive lymph nodes, the study size, and the median duration of follow-up were identified as variables that explained most of the demonstrated data heterogeneity. EAET should be considered as a preferred strategy for high-risk hormone-positive early breast cancer patients with positive lymph nodes; however, the benefit on OS could not be demonstrated.