Olema Oncology’s lead pipeline palazestrant was well tolerated and achieved a median progression-free survival of 4.6 months in the Phase II trial, with the first patient for Phase III to be dosed before the end of this year.

Results from the Phase II trial of Olema’s pipeline drug palazestrant (OP-1250) were positive for the treatment of metastatic ER+/HER2- breast cancer, beating the standards of the EMERALD study, CEO Sean Bohen announced.

The company is using the results, announced in an oral presentation at the European Society for Medical Oncology (ESMO) Congress 2023 in Madrid, Spain, on 22 October 2023, to form plans for its Phase III trial of the candidate.

Further results from the Phase II cohort will be presented after one year following treatment, with the announcement expected at a meeting during H1 2024.

Phase II results

Across the 86 pre-treated patients, 120mg once-daily palazestrant was well tolerated and achieved a median progression-free survival (PFS) of 4.6 months and clinical benefit rate (CBR) of 40%

Patients achieved a median PFS of 5.6 months and CBR of 52% in patients with ESR1 mutations at baseline.

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In the 49 second-line or third-line patients with or without prior chemotherapy, the median PFS was 7.2 months and CBR was 48%. The median PFS was 7.3 months and CBR was 59% for ESR1-mutant patients.

Prior to their participation in the trial, patients were heavily pre-treated with 42% of patients being fourth-line or later at study entry, 65% of patients having received two or more prior lines of endocrine therapy for metastatic disease, and 31% having received prior chemotherapy.

Palazestrant was well tolerated with no dose-limiting toxicities and most treatment-emergent adverse events at Grade I or II. Some patients suffered from gastric events, including nausea and vomiting but the effects were minor and not long-lasting.

Of the 86 patients treated, events of Grade IIII neutropenia were observed in six patients. Of these, three had a dose interruption with recovery and subsequent dose reduction without recurrence. The other three had dose discontinuation followed by recovery.

Phase III trial plans

The Phase III trial, named OPERA-01 will enrol 500 participants from across the globe, with sites in North America, South America, Europe, Australia and parts of Asia, but not China and Japan.

Sites have been activated and enrolment is ongoing, with the first patient to be dosed in the coming weeks.

The primary endpoint will be progression-free survival (PFS). There will be two arms to the trial, palazestrant versus standard of care. All patients will be pre-treated and have used a CDK4/6 inhibitor and endocrine therapy.

Speaking to Clinical Trials Arena, Bohen said that patients in the Phase III study should hopefully not suffer gastric events due to changes in trial design as a result of learning from other combination trials the company is conducting.

“Phase III trial patients can be fed or fasting, unlike Phase II patients who were fasting. Also, they can pick up proton pump inhibitors (PPIs) which they couldn’t in Phase II as we didn’t know what the effects would be,” Bohen explained.

“As a result, we think we’re going to be able to actually not only manage the upper GI but prevent it in the future.”