70-Gene Signature as an Aid to Treatment Decisions in Early Breast Cancer: Updated Results MINDACT

Background: The MINDACT trial showed excellent 5-year distant metastasis-free survival (DMFS) of 94·7% (95%CI 92·5-96·2) in clinical high (C-High)/genomic low (G-Low) risk patients who did not receive chemotherapy. Long-term follow-up is presented. Methods: 6693 patients were enrolled 2007 to 2011. We reassessed DMFS rate at 5 years in C-High/G-Low patients not receiving chemotherapy (n=644) (primary analysis), updated DMFS and overall survival in C-High/G-Low patients receiving chemotherapy or not (n=749 and 748, respectively) (secondary analysis), and examined a potential age effect ( 50y) for women with HR+/HER2- disease. Findings: At a median follow-up of 8·7 years, the updated 5-year DMFS rate for C-High/G-Low patients receiving no chemotherapy is 95·1% (95%CI 93·1-96·6), above the predefined non-inferiority boundary of 92%, proving MINDACT as a positive de-escalation trial.The 5-year and 8-year outcome of C-High/G-Low patients show a respective 0·9% (SE ±1·1) 2·6% (SE ±1·6) difference in DMFS for chemotherapy versus no chemotherapy (HR 0·66; 95%CI 0·48-0·92), without differences in overall survival (95·7% vs 94·3%).The same comparisons confined to HR+/HER2- disease (91% of patients) generate different gain estimates from chemotherapy administration for DMFS according to age: 5% (SE ±2·8%) in women ≤50 years versus 0·2% (SE ±2·3%) in women > 50 years. Interpretation: The clinical utility of a low risk 70-gene signature for foregoing adjuvant chemotherapy in the presence of a high clinical risk (and up to 3 positive nodes) remains proven. In C-high/G-low patients > 50 years chemotherapy did not improve outcome across the whole follow-up trajectory. At longer follow-up in younger women, while underpowered, a clinically relevant benefit of about 5% was observed, possibly due to chemotherapy-induced ovarian function suppression, and should be part of informed, shared decision-making. Trial Registration: ClinicalTrials.gov number, NTC00433589; EudraCT number, 2005-002625-31. Funding Statement: Funded by the European Commission Sixth Framework Programme and other grants. Declaration of Interests: None to declare. Ethics Approval Statement: All patients gave written informed consent. The ethics committees of all participating sites approved the study, which involved collaboration of seven member groups under the Breast International Group umbrella.