Selection of patients with early-stage breast cancer for extended endocrine therapy: secondary analysis of the IDEAL randomized trial

The IDEAL trial randomized postmenopausal patients with HR-positive early-stage breast cancer (EBC) after 5 years of standard adjuvant endocrine therapy to receive 2.5 years or 5 years of extended endocrine therapy (EET). After a median follow-up of 6.5 years, extended endocrine therapy showed no significant benefit on the primary end point of disease-free survival or secondary end points of overall survival and distant metastasis-free survival. Secondary analysis of IDEAL evaluated the 70-gene expression assay MammaPrint for the selection of patients who could benefit from extended endocrine therapy. The figure shows the results of the analysis. Among patients with 70-gene assay-classified low-risk tumors (43.3%), 5 years versus 2.5 years of letrozole was associated with significantly improved distant recurrence risk, which was not seen among patients with high-risk tumors (50.3%) or ultralow-risk tumors (6.4%). As expected, the rates of adverse events and treatment discontinuations were comparable among the different 70-gene assay risk groups in each treatment arm. The authors conclude that the 70-gene assay identified patients with low-risk tumors who could benefit from 5-year versus 2.5-year EET.