PREMIERE parallel, non-comparative, two-arm, randomized 1:1, open-label, multicenter, exploratory window of opportunity study in premenopausal women with primary operable HR+/HER2-negative breast cancer with aiming at evaluating the biological effects of elacestrant with or without triptorelin.

PremiÈRe is a 4-week preoperative WOO randomized 2-arms study with a full program in correlative science, including an accurate estradiol measurement to evaluate the efficacy and biological activity of elacestrant in premenopausal patients with and without OFS (elacestrant 400mg per day during 28 days vs elacestrant at 400 mg per day during 28 days plus triptorelin 3.75mg i.m). Biological information (by tumor biopsy and /or blood sample) will be obtained at baseline, on day 14 (only blood) and day 28 post-treatment. Endpoints as rate of CCCA, mean reduction of Ki67 and estrogen-sensitive signature, allowing comparison of elacestrant activity across populations with and without OFS. Regarding the main objective, rate of CCCA, and considering the eligible population (ki67 between 10-35%) and unpublished data from ELIPSE study we estimate around a 20% of CCCA in all randomized patients. It's worthy to mention that a study using triptorelin as GnRH analog and GCMSMS for E2 measurement showed that nearly all women at day 14 (24 of out 26) had E2 levels in the postmenopausal range26, allowing us to compare groups with and without OFS at that early time-point.