Olema Oncology has announced new data from the phase 1b/2 trial of palazestrant plus ribociclib in ER+/HER2* metastatic breast cancer at the ESMO 2025 Congress. The data shows encouraging activity across all dose cohorts and subgroups. In the 120 mg palazestrant cohort, the median progression-free survival (PFS) was 15.5 months across all patients, with 9.2 months for patients with ESR1 wild-type tumors and 13.8 months for patients with ESR1 mutant tumors. In the 90 mg palazestrant cohort, the median PFS was not reached with a median follow-up of 10.8 months.
As of July 8, 2025, 72 patients were enrolled in the study, with 56 patients receiving 120 mg once-daily palazestrant and 16 patients receiving 90 mg once-daily palazestrant, all with the approved dose of ribociclib for metastatic breast cancer of 600 mg daily. 63% of patients had prior treatment with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy for advanced disease. Of the patients who had prior treatment with CDK4/6i, 33% had an ESR1 mutation at baseline.
The combination of palazestrant and ribociclib demonstrated favorable tolerability and a safety profile consistent with the known profiles of each drug. Across 72 patients treated, both doses of palazestrant combined with ribociclib daily were well tolerated with no new safety signals or increase in toxicity. The majority of treatment-emergent adverse events were grade 1 or 2, consistent with the expected safety profile of each drug.
Dr. Nancy Lin, Associate Chief of the Division of Breast Oncology at the Dana-Farber Cancer Institute, expressed encouragement at the new data, stating that the novel palazestrant-ribociclib combination compares favorably to other endocrine therapy-CDK4/6 inhibitor combinations. She emphasized the potential of palazestrant to serve as an important combination agent in the metastatic setting.
Olema Oncology's President and CEO, Sean P. Bohen, M.D., Ph.D., expressed his satisfaction with the latest data, highlighting the potential of palazestrant to become a best-in-class, backbone endocrine therapy. He also noted the initiation of the phase 3 trial, opera-02, evaluating palazestrant with ribociclib in the frontline setting.
The poster presentation of the data is scheduled for October 20, 2025, at the ESMO Congress. Olema Oncology is committed to transforming the standard of care and improving outcomes for patients living with breast cancer and beyond, with its lead product candidate, palazestrant (OP-1250), currently in two phase 3 clinical trials. Following these announcements, the company's shares moved -16.99%, and are now trading at a price of $7.77. If you want to know more, read the company's complete 8-K report here.
