BOTHELL, Wash., Aug. 14, 2026
LeonaBio, Inc. reported continued progress in the Phase 3 ELAINE-3 clinical trial evaluating lasofoxifene in patients with ER-positive (ER+), HER2-negative, ESR1-mutated metastatic breast cancer. The company has enrolled 495 patients and remains on track to complete enrollment of approximately 600 participants in the fourth quarter of 2026, with topline data expected in the second half of 2027. ELAINE-3 is evaluating lasofoxifene in combination with abemaciclib, a CDK4/6 inhibitor, in patients whose disease has progressed following treatment with aromatase inhibitors and CDK4/6 inhibitors. The registrational study is designed to assess whether the combination can improve progression-free survival (PFS), as determined by blinded independent central review. The advancement of ELAINE-3 represents a key clinical milestone for LeonaBio as it seeks to develop a targeted endocrine treatment for a genetically defined metastatic breast cancer population with limited therapeutic options.
Lasofoxifene Targets ESR1-Mutated Breast Cancer
Lasofoxifene is a third-generation, nonsteroidal selective estrogen receptor modulator (SERM) with a differentiated binding profile designed to maintain activity against both wild-type and mutant estrogen receptors, including clinically important ESR1 mutations associated with resistance to endocrine therapies. LeonaBio is developing the therapy through ELAINE-3 as a potential treatment option for patients with ESR1-mutated metastatic breast cancer after progression on prior endocrine-based treatment. The company previously evaluated lasofoxifene in the ELAINE-1 and ELAINE-2 Phase 2 studies, generating clinical evidence supporting continued development. ELAINE-1 compared lasofoxifene with fulvestrant and reported longer median PFS and higher objective response rates for lasofoxifene, while ELAINE-2 evaluated the combination of lasofoxifene and abemaciclib in heavily pretreated patients. In ELAINE-2, the combination produced a reported median PFS of approximately 13 months, an objective response rate of 56%, and a clinical benefit rate of 65.5%, supporting the rationale for the ongoing Phase 3 program.
ELAINE-3 Enrollment Remains on Track for 2026
The ELAINE-3 Phase 3 trial is the primary clinical focus for LeonaBio as the company moves toward a potentially pivotal readout. The study is designed as a registrational trial in patients with ER-positive, HER2-negative, ESR1-mutated metastatic breast cancer, a population in which acquired endocrine resistance remains a significant treatment challenge. With 495 patients already enrolled, LeonaBio expects to complete enrollment in Q4 2026 and report topline results in 2H 2027. The company is also preparing for potential downstream regulatory and commercial requirements, including CMC, regulatory and commercial readiness activities, while continuing to advance the clinical program. Beyond ELAINE-3, LeonaBio is evaluating the broader potential of lasofoxifene through possible combination strategies and future label expansion opportunities. The company has also continued regulatory and development planning around its second clinical candidate, brelgometon (ATH-1105), an oral, brain-penetrant small molecule being investigated for neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS).
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LeonaBio Maintains Focus on Clinical Development
LeonaBio’s second-quarter update reinforces its strategy of prioritizing late-stage clinical development of lasofoxifene while maintaining longer-term pipeline opportunities. Brelgometon completed a first-in-human Phase 1 study involving 80 healthy volunteers, with results showing a favorable safety and tolerability profile, dose-proportional pharmacokinetics and evidence of central nervous system penetration. The company expects to provide further timing information for a potential Phase 2 proof-of-concept study after completing ELAINE-3 enrollment. Financially, LeonaBio reported $51.1 million in cash, cash equivalents and investments as of June 30, 2026, with second-quarter research and development expenses of $12.9 million, largely reflecting increased ELAINE-3 clinical trial spending. Net loss for the quarter was $19.0 million. With the pivotal breast cancer trial approaching its planned enrollment completion, the key near-term milestones for LeonaBio remain ELAINE-3 enrollment completion in Q4 2026 and the anticipated topline clinical data readout in 2H 2027.
Source:LeonaBio press relese
