Elacestrant in Postmenopausal Women with ER-Positive/HER2-Negative Early Breast Cancer: Findings from the SOLTI-1905-ELIPSE Trial

Elacestrant is the first oral, nonsteroidal, selective estrogen receptor degrader to demonstrate improved efficacy compared to standard of care endocrine therapy in pretreated patients with metastatic breast cancer, with greater relative benefit in ESR1-mutated tumors and a manageable safety profile. SOLTI ELIPSE (NCT04797728) is a prospective, multicenter, window of opportunity trial to assess whether a short course of preoperative elacestrant may suppress tumor proliferation in postmenopausal women with ER-positive/HER2-negative early breast cancer; results of the primary efficacy and safety analysis are reported.

Eligible patients with operable, untreated, ER-positive/HER2-negative breast cancer that were T1c (≥1.5 cm)-T3 and N0, with locally assessed Ki67 ≥10%, received elacestrant 400 mg once daily for 4 weeks. At study completion, patients were treated according to local practice. Centralized assessment of posttreatment (day 28) Ki67 from surgical specimen or tumor biopsy was required for primary end point analysis. Primary efficacy end point was complete cell cycle arrest, defined as Ki67 ≤2.7% at day 28. Ki67 geometric relative change, variation in tumor infiltrating lymphocytes (TILs), switch in PAM50 subtypes, and differential expression of 192 genes from baseline to day 28 were also reported. Adverse events (AEs) were graded according to CTCAE version 5.0.

Between April 2021 and February 2022, 24 patients were enrolled, and 22 patients were evaluated for the primary end point. At day 28, complete cell cycle arrest was achieved in 27% (n = 6) of the patients. Fourteen patients (64%) had day 28 Ki67 ≤10%. A statistically significant 41% Ki67 relative reduction (95% confidence interval, -24 to -58) from baseline to day 28 was observed (P = .007). Overall, elacestrant was associated with a shift towards a more endocrine-sensitive and less proliferative phenotype based on PAM50 gene signatures. Levels of TILs were significantly higher at day 28 (mean difference, +3.73; P = .004). Elacestrant induced high expression of immune-response genes including IGJ, GZMB, CD4, CD8a, suppressed proliferation (eg, UBE2T, MYBL2, BIRC5, MK67), and estrogen-signaling (ESR-1, PGR, CCND1, BRCA2) genes. These changes in gene expression were observed in both tumors with day 28 Ki67 ≤2.7% and those with day 28 Ki67 >10%. Eighty-seven percent of patients reported any-grade AEs, with treatment-related AEs occurring in only 1 patient (grade 3 cutaneous rash), which led to discontinuation. Most frequently reported AEs (all grade 1) were hot flash (n = 6), dyspepsia (n = 2), anemia (n = 2), and constipation (n = 2). No serious AEs were reported.

Investigators concluded that, in patients with untreated ER-positive/HER2-negative early breast cancer, a short preoperative course of treatment with elacestrant was associated with relevant biological and molecular responses, with a manageable safety profile. These findings support further investigation of preoperative elacestrant in early breast cancer.

Source:

Vidal M, Pascual T, Falato C, et al. Elacestrant in postmenopausal women with estrogen receptor positive and HER2-negative early breast cancer: primary efficacy and safety analysis of the pre-operative, window of opportunity SOLTI-1905-ELIPSE trial. San Antonio Breast Cancer Symposium 2022. Abstract PD13-01.