On April 11, 2025 Sermonix Pharmaceuticals Inc., a privately held biopharmaceutical company developing innovative therapeutics to specifically treat metastatic breast cancers (mBC), and Quantum Leap Healthcare Collaborative reported that in the Phase 2 clinical trial evaluating lasofoxifene as a neoadjuvant endocrine therapy in molecularly selected HR+/HER2-, locally advanced breast cancer, the investigational drug was well tolerated and demonstrated promising early activity in suppressing the Ki67 protein in both premenopausal and postmenopausal patients (Press release, Sermonix Pharmaceuticals, APR 11, 2025, View Source [SID1234651888]).
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Results from the study, an arm of the Endocrine Optimization Pilot Protocol (EOP), a sub-study of Quantum Leap’s ongoing I-SPY 2 TRIAL (Investigation of Serial studies to Predict Your Therapeutic Response with Imaging And moLecular analysis 2), were initially shared yesterday in a poster presentation at RISE UP for Breast Cancer.
Twenty patients (10 pre- and nine postmenopausal women, and one male) were enrolled in the lasofoxifene arm of the study, during which early Ki67 suppression in premenopausal patients was seen in the absence of ovarian function suppression (OFS). Ki67 is a marker that measures how fast cancer cells are dividing.
"Lasofoxifene continued to demonstrate a strong tolerability profile while showing promising Ki67 suppression in this Phase 2 study, supporting our plans to further explore its potential in the neoadjuvant setting," said Dr. David Portman, Sermonix founder and chief executive officer. "We are currently studying lasofoxifene in the ELAINE-3 Phase 3 combination study with abemaciclib in the ESR1-mutated metastatic breast cancer setting. We are excited to see it continue to demonstrate broad potential while offering unique quality of life benefits for people confronted with breast cancer."
Patients were enrolled in the I-SPY 2 arm from March 2023 to May 2024. Median total days of treatment was 154 days. At the time of data analysis, three patients were still on treatment and two discontinued treatment due to physician or patient preference.
Median Ki67 expression went from 10% at baseline (range 1.0-40%) to 4% (1.0-18.0%) at Week 3. At three weeks, Ki67 expression was suppressed to <10% in 14 out of 16 (88%) patients, and to <2.7% in 6 out of 16 (38%) patients. Adverse events (AEs) were all grade 1-2. Most common AEs include hot flushes (65%), constipation (40%), fatigue (40%) and nausea (25%).
"The I-SPY 2 EOP provides a biomarker-rich platform to test novel endocrine agents in the neoadjuvant setting in a molecularly selected group of patients with tumors that are predicted to have little to no benefit from chemotherapy," said Dr. Jo Chien, principal investigator of the sub-study. "Lasofoxifene has demonstrated significant activity based on early Ki67 suppression, not only in postmenopausal women, but also in 10 premenopausal women without concomitant ovarian function suppression, with baseline Ki67 of 12.5% (1.0-40.0%) going to 3.0% (1.0-15%) at Week 3. It is exciting to see that lasofoxifene is well-tolerated even in our youngest patients who are often most impacted by the debilitating side effects of current standard endocrine therapy options."
Quantum Leap partners with a consortium that includes the U.S. Food and Drug Administration (FDA), industry, patient advocates, philanthropic sponsors and clinicians from 41 major U.S. cancer research centers.
About Lasofoxifene
Lasofoxifene is an investigational novel endocrine therapy in clinical development which has demonstrated robust target engagement as an ESR1 antagonist in the breast, particularly in the presence of ESR1 mutations. Lasofoxifene has demonstrated anti-tumor activity as monotherapy and in combination with a CDK4/6 inhibitor in Phase 2 studies and has unique tissue selectivity distinguishing it from other current and investigational endocrine therapies, with beneficial effects seen on vagina and bone in previous clinical studies. Lasofoxifene, which Sermonix licensed globally from Ligand Pharmaceuticals Inc., has been studied in previous comprehensive Phase 1-3 non-oncology clinical trials in more than 15,000 postmenopausal women worldwide. Lasofoxifene’s bioavailability and activity in mutations of the estrogen receptor could potentially hold promise for patients who have acquired endocrine resistance due to ESR1 mutations, a common finding in the metastatic setting and an area of high unmet medical need. Lasofoxifene’s novel activity in ESR1 mutations was discovered at Duke University and Sermonix has exclusive rights to develop and commercialize the product in this area. Lasofoxifene, a novel targeted and tissue selective oral endocrine therapy, could, if approved, play a critical role in the precision medicine treatment of advanced ER+ breast cancer.