On October 18, 2025 Olema Pharmaceuticals, Inc. ("Olema" or "Olema Oncology", Nasdaq: OLMA), a clinical-stage biopharmaceutical company focused on the discovery, development, and commercialization of targeted therapies for breast cancer and beyond, reported updated data from the Phase 1b/2 study of palazestrant in combination with ribociclib in patients with estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer. These findings will be presented in a poster session on October 20 at the European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) Congress 2025 in Berlin, Germany.

Schedule your 30 min Free 1stOncology Demo!
Discover why more than 1,500 members use 1stOncology™ to excel in:

Early/Late Stage Pipeline Development - Target Scouting - Clinical Biomarkers - Indication Selection & Expansion - BD&L Contacts - Conference Reports - Combinatorial Drug Settings - Companion Diagnostics - Drug Repositioning - First-in-class Analysis - Competitive Analysis - Deals & Licensing

                  Schedule Your 30 min Free Demo!

"We are very pleased with these latest data showing compelling progression-free survival and favorable tolerability of palazestrant plus ribociclib, further reinforcing this regimen’s potential as a new standard of care in metastatic breast cancer," said Sean P. Bohen, M.D., Ph.D., President and Chief Executive Officer of Olema Oncology. "These data showcase the activity of the combination in both ESR1 mutant and wild-type tumors, an important component for effective frontline treatment, and underscore the importance of complete ER antagonism in the treatment of ER-positive breast cancer. As we work to transform the breast cancer treatment paradigm, we are increasingly confident in palazestrant’s potential to become a best-in-class, backbone endocrine therapy and are excited to now have our second Phase 3 trial, OPERA-02, underway evaluating palazestrant with ribociclib in the frontline setting."

Key Findings from the Phase 1b/2 Study of Palazestrant in Combination with Ribociclib
As of July 8, 2025, 72 patients were enrolled across the 90 mg and 120 mg palazestrant dose cohorts. 56 patients received 120 mg once-daily palazestrant and 16 patients received 90 mg once-daily palazestrant, all with the approved dose of ribociclib for metastatic breast cancer of 600 mg daily. 45 (63%) patients had prior treatment with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy for advanced disease. 33% (15/45) of patients who had prior treatment with CDK4/6i in the advanced setting (2/3L) had an ESR1 mutation at baseline.

Efficacy

In the 90 mg palazestrant dose cohort, with a median follow-up of 10.8 months, median progression-free survival (PFS) was not reached.
In the 120 mg palazestrant dose cohort, with a median follow-up of more than 19 months, median PFS are mature. Median PFS was 15.5 months for all patients. Median PFS was 12.2 months for those who received prior treatment with CDK4/6i, including 9.2 months for patients with ESR1 wild-type tumors and 13.8 months for patients with tumors with ESR1 mutations.

Safety and Pharmacokinetics

Across 72 patients treated, 90 mg or 120 mg of palazestrant combined with 600 mg of ribociclib daily was well tolerated with no new safety signals or increase in toxicity.
Palazestrant and ribociclib did not demonstrate any drug-drug interactions and the overall safety profile was consistent with the established safety profile of ribociclib plus an endocrine therapy.
The majority of treatment-emergent adverse events were grade 1 or 2, and the severity and incidence of adverse events were consistent with the expected safety profile of each drug.

"Despite recent advances in the treatment of ER+/HER2- metastatic breast cancer, there remains a significant need for therapies that can overcome endocrine resistance, particularly following treatment with a CDK4/6 inhibitor," said Dr. Nancy Lin, Associate Chief of the Division of Breast Oncology, Susan F. Smith Center for Women’s Cancers, at the Dana-Farber Cancer Institute. "I am very encouraged by these new data showing the novel palazestrant-ribociclib combination compares favorably to other endocrine therapy-CDK4/6 inhibitor combinations. With a compelling median PFS in the challenging post-CDK4/6 inhibitor setting, I believe palazestrant has the potential to serve as an important combination agent in the metastatic setting."

Poster Presentation Details
Title: Palazestrant (OP-1250) plus ribociclib in patients with estrogen receptor-positive,
human epidermal growth factor receptor 2-negative (ER+, HER2-) advanced breast cancer (ABC)
Poster Number: 502P
Session: Breast Cancer, Metastatic Session
Date/Time: Monday, October 20, 2025, from 12:00-12:45pm CEST / 6:00-6:45am ET

Additional information can be found on the ESMO (Free ESMO Whitepaper) 2025 website, including abstracts. A copy of the poster will be made available on the Publications page of Olema’s website in alignment with the ESMO (Free ESMO Whitepaper) 2025 embargo policy.

(Press release, Olema Oncology, OCT 18, 2025, View Source [SID1234656776])