Clinical outcomes comparison of 10 years versus 5 years of adjuvant endocrine therapy in patients with early breast cancer

Background: Adjuvant endocrine therapy undoubtedly prolongs the time to recurrence for patients with hormone-positive early breast cancer. Extended endocrine therapy to 10 years or longer has been expected to bring a greater clinical advantage. However, the related research conclusions are controversial.

Methods: Tamoxifen (TAM), Aromatase Inhibitor (AI), Exemestane, letrozole (LET) and anastrozole were used as key words in the literature search. After the patients completed 5 years of adjuvant endocrine treatment, they were allocated to continue endocrine treatment for 5 years or receive placebo/observation for 5 years. Disease-free survival (DFS) and overall survival (OS) were the end points. Systematic assessment was performed using Stata 12.0.

Results: Twelve trials including 30,848 cases were involved. The overall analysis demonstrated that extended endocrine therapy to 10 years significantly prolonged DFS compared with 5 years of endocrine therapy [hazard ratio (HR) = 0.84, 95% CI: 0.73-0.97]. Subgroup analysis showed that DFS was significant prolonged with TAM 5y - AI 5y treatment versus TAM 5y treatment and with (AI and/or TAM) 5y - LET 5y treatment versus (AI and/or TAM) 5y treatment [(HR = 0.61, 95% CI: 0.50-0.76) and (HR = 0.81, 95% CI: 0.71-0.93), respectively]. However, no significant difference was found in the DFS with TAM 5y - TAM 5y treatment versus TAM 5y treatment (HR = 0.97, 95% CI: 0.81-1.17). Overall and subgroup analysis did not demonstrate an OS benefit of therapy extended to 10 years. A DFS benefit of extended endocrine therapy to 10 years was verified in the lymph node-positive subgroup, postmenopausal subgroup and ER+ and/or PR+ subgroup (HR = 058, 95% CI: 0.45-0.75; HR = 0.70, 95% CI: 0.58-0.80; HR = 0.80, 95% CI: 0.67-0.96).

Conclusions: An extended 10 years of endocrine treatment yields a DFS benefit for patients with early breast cancer; (AI and/or TAM) 5y - AI 5y treatment is the optimal choice. ER+ and/or PR+, postmenopausal and lymph node-positive patients are the most suitable groups.