Menarini Group Presents Updated Results from Pivotal Phase 3 EMERALD Trial at the 2022 San Antonio Breast Cancer Symposium (SABCS) that Demonstrate Elacestrant’s PFS Increases with Duration of Prior CDK4/6i in ER+, HER2- in Metastatic Setting

• Elacestrant demonstrated longer progression-free survival (PFS) vs SOC endocrine therapy with medians up to 8.6 months, positively associated with the duration of prior treatment with CDK4/6 inhibitors
• Elacestrant side effects were manageable and consistent with previously reported results
• Results demonstrate that elacestrant may have the potential to become a new standard of care as a monotherapy endocrine sequencing option in ER+, HER2- advanced or metastatic breast cancer after progression on CDK4/6i

The Menarini Group (“Menarini”), a privately held Italian pharmaceutical and diagnostics company, and Stemline Therapeutics (“Stemline”), a wholly-owned subsidiary of the Menarini Group, will present additional data from the Phase 3 EMERALD study (NCT03778931) of elacestrant, an investigational oral SERD, during the upcoming San Antonio Breast Cancer Symposium (SABCS) being held from December 6-10.

EMERALD is a Phase 3 registrational trial that demonstrated statistically significant progression-free survival (PFS) with elacestrant vs SOC endocrine monotherapy (fulvestrant, letrozole, anastrozole, exemestane), meeting both primary endpoints in all patients and in those patients harbouring ESR1 mutations (ESR1-mut), following progression on prior CDK4/6 inhibitors (CDK4/6i) in ER+, HER2- advanced or metastatic breast cancer.

A post-hoc analysis of the PFS results in the EMERALD trial based on the duration of prior CDK4/6i usage shows clinically meaningful results which favor monotherapy elacestrant, both in the total patient population as well as in patients with ESR1-mut. Increased duration of prior CDK4/6i in metastatic patients was positively associated with longer PFS on elacestrant but not with SOC.

For those who were exposed to CDK4/6i ≥12 months prior to randomization on EMERALD, elacestrant achieved:

• In the all-patient population, a mPFS of 3.8 months on elacestrant vs 1.9 months on SOC, a 39% reduction in the risk of progression or death (HR=0.61 95% CI: 0.45-0.83)
• In the ESR1-mut population, a mPFS of 8.6 months on elacestrant vs 1.9 months on SOC, a 59% reduction in the risk of progression or death (HR=0.41 95% CI: 0.26-0.63)

For those who were exposed with CDK4/6i ≥18 months prior to randomization on EMERALD, elacestrant achieved:

• In the all-patient population, a mPFS of 5.5 months on elacestrant vs 3.3 months with SOC, a 30% reduction in the risk of progression or death (HR=0.70 95% CI: 0.48-1.02)
• In the ESR1-mut population, a mPFS of 8.6 months on elacestrant vs 2.1 months on SOC, a 53% reduction in the risk of progression or death (HR=0.47 CI: 0.20-0.79).

Updated safety data were consistent with previously reported results. Most of the adverse events (AEs), including nausea, were grade 1 and 2, and only 3.4% and 0.9% of the patients discontinued trial therapy because of an AE on elacestrant and SOC, respectively. A low percentage of patients received an antiemetic; 8.0% on elacestrant, 3.7% on fulvestrant, and 10.3% on AI, respectively. No hematological safety signal was observed and none of the patients in either of the two treatment arms had sinus bradycardia.

Virginia Kaklamani, MD, DSc, breast medical oncologist and professor of medicine, UT Health San Antonio, MD Anderson Cancer Center, commented, “These results show that when used as a single agent, elacestrant provided mPFS up to 8.6 months, based on the duration of previous CDK4/6 inhibitor therapy, with a manageable safety profile and the convenience of an oral tablet. This suggests elacestrant may have the potential to become a new standard of care as a monotherapy endocrine sequencing option in ER+, HER2- advanced breast cancer after progression on CDK4/6i, before moving to combination therapies.”

“These results further highlight elacestrant’s potential to change the treatment paradigm of ER+, HER2- advanced or metastatic breast cancer. Elacestrant is under Priority Review with the U.S. Food and Drug Administration (FDA) with a target PDUFA date of February 17, 2023,” commented Elcin Barker Ergun, Chief Executive Officer of the Menarini Group.