The optimal duration and selection of adjuvant endocrine therapy for breast cancer: how long is enough?

Women with estrogen receptor (ER)+ early breast cancer (BC) are at continuing risk of relapse up to at least 15 years after diagnosis, despite being on adjuvant endocrine therapy for approximately 5 years. Extended adjuvant endocrine therapy with an aromatase inhibitor (AI) after 5 years of tamoxifen further reduces the risk of recurrence in postmenopausal women. More recently, continuing tamoxifen for 10 years has also been shown to further reduce the risk of recurrence compared with 5 years. There are no direct comparative data on the relative merits of extended tamoxifen compared with an AI; indirect evidence suggests that an AI may have increased efficacy but a greater adverse effect on quality of life. Results are awaited on the need for continuing front-line adjuvant AIs for more than 5 years. The next challenge is to determine which patients will benefit from this long-term treatment. Currently, tumor size, nodal involvement, and gene expression profile as measured by the PAM50 Risk of Recurrence (ROR) score have all been shown to have prognostic significance for late recurrence beyond 5 years.