Effectiveness of Adding Everolimus to the First-line Treatment of Advanced Breast Cancer in Premenopausal Women Who Experienced Disease Progression While Receiving Selective Estrogen Receptor Modulators

IMPORTANCE: The effectiveness of the mammalian target of rapamycin (mTOR) inhibitor everolimus in premenopausal women with hormone receptor (HR)-positive/ERBB2-negative advanced breast cancer who experienced disease progression while receiving selective estrogen receptor modulators (SERMs) is unknown. OBJECTIVE: To compare the effectiveness of everolimus plus letrozole vs letrozole alone in premenopausal women with HR-positive/ERBB2-negative advanced breast cancer who experienced disease progression while receiving SERMs. DESIGN, SETTING, AND PARTICIPANTS: The Everolimus Trial for Advanced Premenopausal Breast Cancer (MIRACLE) was a multicenter, open-label phase 2 randomized clinical trial of everolimus plus letrozole vs letrozole alone as first-line treatment conducted from December 8, 2014, to September 26, 2018. Participants included premenopausal women with HR-positive, ERBB2-negative advanced breast cancer who experienced disease progression while receiving SERMs. Analysis was performed on an intent-to-treat basis from January 5, 2015, to December 30, 2019. EXPOSURES: Patients were randomly assigned in a 1:1 ratio to receive everolimus (10 mg orally once daily) plus letrozole (2.5 mg orally once daily) (n = 101) or letrozole alone (2.5 mg orally once daily) (n = 98). Both groups received goserelin, 3.6 mg, subcutaneously on day 1 of each 28-day cycle. Patients in the letrozole group were permitted to cross over to receive everolimus with letrozole if disease progression occurred. MAIN OUTCOMES AND MEASURES: The primary end point was progression-free survival (PFS), defined as the time from randomization to confirmed disease progression or death due to any cause. RESULTS: A total of 199 women (mean [SD] age, 44.3 [6.3] years) were randomized. Patients receiving everolimus plus letrozole achieved a significantly longer median PFS compared with those receiving letrozole alone (19.4 months [95% CI, 16.3-22.0 months] vs 12.9 months [95% CI, 7.6-15.7 months]; hazard ratio, 0.64 [95% CI, 0.46-0.89]; P = .008). A total of 56 of the 98 patients in the letrozole group (57.1%) were crossed over to also receive everolimus. The median PFS after crossover was 5.5 months (95% CI, 3.8-8.2 months). CONCLUSIONS AND RELEVANCE: In this randomized clinical trial, PFS was significantly longer among premenopausal patients with HR-positive/ERBB2-negative advanced breast cancer who received everolimus plus letrozole than among those who received letrozole alone. The results revealed that everolimus was effective even among patients receiving treatment with the same endocrine agent after disease progression. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02313051.