• Encouraging safety and preliminary efficacy analysis from the elacestrant and capivasertib Phase 1b regimen of the ELEVATE study will be presented.
• The efficacy data highlight how the combination of elacestrant and capivasertib has the potential to address key resistance mechanisms for patients with ER+/HER2- mBC, including ESR1 and PIK3CA co-existing mutations.
• The company will also share updates on its elacestrant clinical development program, underscoring its potential in both mBC combination settings and as a monotherapy in early breast cancer.

FOR MEDICAL AND PHARMACEUTICAL TRADE MEDIA ONLY

FLORENCE, Italy and NEW YORK, May 28, 2026 /PRNewswire/ -- The Menarini Group ("Menarini"), a leading international pharmaceutical and diagnostics company, and Stemline Therapeutics, Inc. ("Stemline"), a wholly-owned subsidiary of the Menarini Group, focused on bringing transformational oncology treatments to cancer patients, will present safety and preliminary efficacy for the elacestrant and capivasertib combination arm of the Phase 1b/2 ELEVATE study in patients with estrogen receptor-positive (ER+), HER2-negative (HER2-) locally advanced or metastatic breast cancer (mBC). Additionally, various other trial-in-progress updates will be presented, underscoring elacestrant's potential as an endocrine therapy (ET) backbone across the spectrum of breast cancer. These data will be presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting.

The ELEVATE study was designed to evaluate the safety and efficacy of combination treatment options with elacestrant, to overcome different resistance mechanisms observed in ER+/HER2- mBC and improve patient outcomes, irrespective of ESR1 mutation status. The study is composed of six treatment regimens evaluating elacestrant in combination with CDK4/6 inhibitors (palbociclib, abemaciclib and ribociclib) and with inhibitors of the PI3K/AKT/mTOR pathway (everolimus, alpelisib and capivasertib).

ELEVATE results reported at ASCO 2026 (abstract 1098)^[1] include safety and preliminary efficacy data from the phase 1b elacestrant (258-345 mg) plus capivasertib (320-400 mg) cohorts (n=31), which demonstrate preliminary median progression-free survival (mPFS) benefit in the recommended phase 2 dose (RP2D) cohort. The RP2D was determined in cohort 2 (n=9) to be elacestrant 345 mg plus capivasertib 320 mg BID (4 days on/3 days off).

In RP2D response-evaluable patients, preliminary efficacy showed an 88.9% disease control rate (DCR), a 66.7% clinical benefit rate at 24 weeks (CBR24), and a 33.3% objective response rate (ORR). All patients with ORR had co-existing ESR1 and PIK3CA mutations. The median duration of response (mDOR) has not yet been reached.  The preliminary mPFS was 11.3 months in the overall RP2D population, and 10.9 months in patients with co-existing ESR1 and PIK3CA mutations. Additionally, these initial results show that the combination is consistent with the known safety profiles of each targeted therapy plus standard of care endocrine therapy.

"The combination of elacestrant plus capivasertib is designed to address an unmet need for patients with ER+/HER2- PI3K-pathway altered metastatic breast cancer, particularly when co-existing ESR1 and PIK3CA mutations are present." said Sara Tolaney, MD, MPH, Chief of the Division of Breast Oncology, Dana-Farber Cancer Institute.  "These encouraging preliminary data suggest the potential for extended clinical benefit with a manageable safety profile, as the combination regimen could simultaneously target ESR1 and PIK3CA mutations, potentially avoiding the need for sequential regimens that address each target individually."

"Building on the data we saw last year at SABCS, we continue to be encouraged by elacestrant's potential clinical benefit observed across numerous combinations with different agents targeting ER+/HER2- metastatic breast cancer," said Elcin Barker Ergun, CEO of the Menarini Group. "The breadth of our studies, including early breast cancer and various combinations for ER+/HER2- metastatic breast cancer, including with capivasertib, demonstrate our commitment to bringing potentially transformational therapies to cancer patients."

In addition, other elacestrant data will be presented at the ASCO congress. See below for a complete list of upcoming presentations:

Presentation Title: Elacestrant in combination with capivasertib in patients with ER+/HER2- advanced breast cancer: Update from ELEVATE, a phase 1b/2 open-label, umbrella study
Abstract Number: 1098
Presentation Date & Time: June 1, 2026; 1:30 – 4:30 PM CT
Location: Poster Board 212
Presenting Author: Wassim McHayleh

Presentation Title: ADELA: A double-blind, placebo-controlled, randomized phase 3 trial of elacestrant + everolimus versus elacestrant + placebo in ER+/HER2- advanced breast cancer patients with ESR1-mutated tumors progressing on endocrine therapy + CDK4/6i*#
Abstract Number: TPS1154
Presentation Date & Time: June 1, 2026; 1:30 – 4:30 PM CT
Location: Poster Board 262b
Presenting Author: Antonio Llombart-Cussac

Presentation Title: ELECTRA: An open-label, multicenter, phase 1b/2 study of elacestrant in combination with abemaciclib in patients with brain metastasis from ER+/HER2- breast cancer
Abstract Number: TPS1155
Presentation Date & Time: June 1, 2026; 1:30 – 4:30 PM CT
Location: Poster Board 263a
Presenting Author: Nuhad Ibrahim

Presentation Title: CAPELA: A phase II multicenter open-label randomized study of capecitabine in combination with elacestrant versus capecitabine alone in advanced estrogen receptor (ER)–positive breast cancer (TBCRC 070)*
Abstract Number: TPS1156
Presentation Date & Time: June 1, 2026; 1:30 – 4:30 PM CT
Location: Poster Board 263b
Presenting Author: Kristina Fanucci

Presentation Title: ELEGANT: Elacestrant versus standard endocrine therapy in women and men with node-positive, estrogen receptor-positive (ER+), HER2-negative (HER2-), early breast cancer with high risk of recurrence in a global, multicenter, randomized, open-label phase 3 study
Abstract Number: TPS1153
Presentation Date & Time: June 1, 2026; 1:30 – 4:30 PM CT
Location: Poster Board 262a
Presenting Author: Aditya Bardia

*Denotes investigator sponsored research or collaborative research

#The ADELA study is a pivotal study co-sponsored with MEDSIR

About The Elacestrant Clinical Development Program

Elacestrant is also being investigated in several company-sponsored clinical trials in metastatic breast cancer disease, alone or in combination with other therapies. ELEVATE (NCT05563220) is a phase 1b/2 clinical trial evaluating the safety and efficacy of elacestrant combined with alpelisib, everolimus, capivasertib, palbociclib, ribociclib or abemaciclib. ELECTRA (NCT05386108) is an open-label phase 1b/2, multicenter study evaluating elacestrant in combination with abemaciclib in patients with ER+, HER2- breast cancer. The phase 2 portion evaluates this treatment regimen in patients with brain metastases. ELCIN (NCT05596409) is a phase 2 trial evaluating the efficacy of elacestrant in patients with ER+, HER2- advanced/metastatic breast cancer who received one or two prior hormonal therapies and no prior CDK4/6 inhibitors in the metastatic setting. ADELA (NCT06382948) is a phase 3 randomized, double-blinded trial evaluating elacestrant in combination with everolimus in patients with ER+, HER2- mBC with ESR1-mut tumors. ELEGANT (NCT06492616) is a phase 3 trial evaluating the effectiveness of elacestrant versus standard endocrine therapy in women and men with node-positive, ER+, HER2- early breast cancer with high risk of recurrence. Elacestrant is also being evaluated in additional investigator-led trials, in trials conducted in collaboration with other companies, in metastatic breast cancer as well as in early disease.

To report SUSPECTED ADVERSE REACTIONS, contact Stemline Therapeutics, Inc. at adverseevents@menarinistemline.com. All of the relevant information can be found at https://stemline.com/contact/

Full prescribing information for elacestrant can be found at https://www.ema.europa.eu/en/medicines/human/EPAR/orserdu#product-info

About The Menarini Group

The Menarini Group is a leading international pharmaceutical and diagnostics company, with a turnover of $5.5 billion and over 17,000 employees. Menarini is focused on therapeutic areas with high unmet needs with products for cardiology, oncology, pneumology, gastroenterology, infectious diseases, diabetology, inflammation, and analgesia. With 18 production sites and 9 Research and Development centers, Menarini's products are available in 140 countries worldwide. For further information, please visit www.menarini.com.

About Stemline Therapeutics Inc.
Stemline Therapeutics, Inc. ("Stemline"), a wholly-owned subsidiary of the Menarini Group, is a commercial-stage biopharmaceutical company focused on bringing transformational oncology treatments to patients. Stemline commercializes elacestrant, an oral endocrine therapy indicated for the treatment of postmenopausal women or adult men with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, ESR1-mutated advanced or metastatic breast cancer with disease progression following at least one line of endocrine therapy, in the U.S., Europe, and other global regions. Stemline also commercializes tagraxofusp-erzs, a novel targeted therapy directed to CD123, for patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN), an aggressive hematologic cancer, in the United States, Europe, and other global regions. In addition, Stemline commercializes selinexor, an XPO1 inhibitor for multiple myeloma, in Europe. The company is also conducting multiple label-expansion studies with elacestrant and tagraxofusp in breast and hematologic cancer indications, respectively, and has an extensive clinical pipeline of additional drug candidates in various stages of development for a host of solid and hematologic cancers.

[1] The safety and efficacy of the investigational combinations and unapproved indications discussed in this press release have not been established by the FDA, EMA, or any other regulatory authority.

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