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Exhibit 99.1

LeonaBio Reports Second Quarter 2026 Financial Results and Provides Business Update

On Track to Complete Enrollment of Phase 3 ELAINE-3 Clinical Trial of Lasofoxifene in ER-positive (ER+), HER2-negative, ESR1-mutated Metastatic Breast Cancer in 4Q 2026 with Topline Data Expected in 2H 2027

BOTHELL, Wash., August 14, 2026 – LeonaBio, Inc. (NASDAQ: LONA), a clinical-stage biopharmaceutical company dedicated to the development of novel therapeutics for diseases with high unmet medical needs, today reported financial results for the quarter ended June 30, 2026, and provided recent pipeline and business updates.

“We enter the second half of 2026 with a clear focus on executing our Phase 3 ELAINE-3 trial and advancing lasofoxifene toward what we believe could be a transformative treatment option for patients with ESR1-mutated metastatic breast cancer,” said Mark Litton, Ph.D., President and Chief Executive Officer of LeonaBio. “We have enrolled 495 patients and remain on track to complete enrollment of ELAINE-3 in the fourth quarter of 2026 with topline data expected in the second half of 2027. As the treatment landscape for metastatic breast cancer continues to evolve, we believe the differentiated profile of lasofoxifene positions it to address a significant unmet need as a potential endocrine therapy partner and create opportunities beyond ELAINE-3, including additional combination strategies and future label expansions. The body of clinical and scientific evidence behind lasofoxifene supports our confidence in its potential to greatly benefit patients battling this difficult-to-treat form of breast cancer.”

“As we approach the completion of enrollment in this Phase 3 registrational trial, we are investing today in critical CMC, regulatory, and commercial readiness activities to ensure we are well-positioned to bring this therapy to patients as quickly as possible, if approved. With our talented team and the potential to add up to an additional $146 million upon exercise of cash-exercisable warrants issued in our December 2025 financing, we believe LeonaBio is well-positioned to deliver on multiple value-creating milestones in the years ahead,” added Dr. Litton.

Clinical Development & Pipeline Programs

Lasofoxifene – A third generation novel, nonsteroidal selective estrogen receptor modulator (SERM) with a unique binding profile, designed to confer potent activity against both wild-type and mutant estrogen receptors, including the clinically significant ESR1 mutations commonly associated with resistance to endocrine therapy in metastatic breast cancer.

In December 2025, LeonaBio acquired an exclusive global license (excluding Asia and certain countries in the Middle East) from Sermonix Pharmaceuticals, Inc. for rights to develop and commercialize lasofoxifene.

• Lasofoxifene is being advanced in ELAINE-3, a Phase 3 clinical trial (NCT05696626), in combination with abemaciclib, a CDK4/6 inhibitor, as a targeted therapy for estrogen receptor-positive (ER+), HER2-negative, ESR1-mutated metastatic breast cancer, following progression on

aromatase inhibitors and CDK4/6 inhibitors. The primary endpoint of the study is a statistically significant improvement in progression free survival (PFS), as determined by blinded, independent central review (BICR). ELAINE-3 aims to establish a new standard of care for this genetically defined patient group with limited treatment options.

• The Company expects to complete enrollment of ~600 participants in the Phase 3 ELAINE-3 clinical trial in the fourth quarter of 2026 and to have topline data in the second half of 2027.

• Lasofoxifene was previously evaluated in two Phase 2 studies in patients with ER+, HER2-negative locally advanced or metastatic breast cancer expressing an ESR1 mutation, ELAINE-1 and ELAINE-2.

o ELAINE-1, an open-label, randomized trial comparing lasofoxifene to fulvestrant, showed improved outcomes for lasofoxifene as a potential monotherapy. Although the trial was not powered, results included longer median progression-free survival (5.6 vs. 3.7 months), higher objective response rates (13.3% vs. 2.9%) and a durable complete response lasting more than 2.5 years. The treatment was well-tolerated with patients reporting quality-of-life benefits.

o ELAINE-2, an open-label study evaluating lasofoxifene in combination with abemaciclib, demonstrated clinical benefits in heavily pretreated patients, with a median progression-free survival of approximately 13 months, an objective response rate of 56% and a clinical benefit rate of 65.5%. The combination was generally well-tolerated with most adverse events being low grade.

• In April 2026, LeonaBio hosted a virtual Key Opinion Leader event with two leading physicians in the breast cancer field to discuss the current and evolving treatment landscape in metastatic breast cancer and the potential for lasofoxifene to transform the standard of car

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Exhibit 99.1

LeonaBio Reports First Quarter 2026 Financial Results and Provides Business Update

Advancing Phase 3 Lasofoxifene Development Program of Novel Selective Estrogen Receptor Modulator, a Potential Multi-Billion Dollar Opportunity as Treatment Option for Patients with ESR1-Mutations

Expects to Complete Enrollment of Phase 3 Clinical Trial of Lasofoxifene in treatment-resistant ER-positive, HER2-negative, ESR1-mutated Metastatic Breast Cancer in 4Q 2026 with Topline Data Anticipated in 2H 2027

On-track to Initiate Phase 2 Proof-of-Concept Study of ATH-1105 in ALS patients in 2H 2026

Recent Events Include Three Appointments to Board of Directors and Virtual Key Opinion Leader Event Highlighting Potential of Lasofoxifene

BOTHELL, Wash., May 7, 2025 – LeonaBio, Inc.(NASDAQ: LONA), a clinical-stage biopharmaceutical company dedicated to the development of novel therapeutics for diseases with high unmet medical needs, today reported financial results for the quarter ended March 31, 2026, and provided recent pipeline and business updates.

“We entered 2026 with a clear focus on disciplined execution across our portfolio, led by the continued advancement of lasofoxifene in the Phase 3 ELAINE‑3 clinical trial for patients with ESR1‑mutated metastatic breast cancer, a population with significant unmet need,” said Mark Litton, Ph.D., President and Chief Executive Officer of LeonaBio. “As the treatment landscape continues to evolve, we remain confident in the ELAINE‑3 program, supported by a body of nonclinical and clinical evidence that we believe reinforces lasofoxifene’s differentiated profile and its potential to meaningfully address endocrine resistance, including independent mechanistic data from animal models on its bone protective potential, which further strengthens our conviction in the scientific and clinical rationale underlying this pivotal study.”

“In parallel, we are continuing to advance ATH‑1105 toward a Phase 2 proof‑of‑concept trial in amyotrophic lateral sclerosis (ALS), building on encouraging Phase 1 data demonstrating a favorable safety profile, pharmacokinetics, and central nervous system (CNS) penetration,” continued Dr. Litton. “With a strengthened balance sheet following our December 2025 $90 million common stock and warrant financing together with the potential additional $146 million upon exercise of the cash-exercisable warrants, we believe we are well positioned to execute on multiple value‑creating milestones in 2026 and beyond as we work to bring transformative therapies to patients in urgent need of new medicines.”

Clinical Development & Pipeline Programs

Lasofoxifene – A novel, nonsteroidal selective estrogen receptor modulator (SERM) with a unique binding profile, designed to act as a potent antagonist against breast wild-type and mutant estrogen receptors, including the clinically significant ESR1 mutations commonly associated with resistance to endocrine therapy in metastatic breast cancer, while preserving estrogen signaling in nontarget tissues such as bone.

In December 2025, LeonaBio acquired an exclusive global license (excluding Asia and certain countries in the Middle East) from Sermonix Pharmaceuticals, Inc. (Sermonix) for rights to develop and commercialize lasofoxifene.

• Lasofoxifene is being advanced in a Phase 3 clinical trial (NCT05696626) in combination with abemaciclib, a CDK4/6 inhibitor, as a targeted therapy for estrogen receptor-positive (ER+), HER2-negative, ESR1-mutated metastatic breast cancer, a population with limited treatment options following progression on aromatase inhibitors and CDK4/6 inhibitors. The primary endpoint of the study is a statistically significant improvement in progression free survival (PFS) as determined by blinded, independent central review (BICR). The ongoing Phase 3 trial aims to establish a new standard of care for this genetically defined patient group.

• LeonaBio is amending the ELAINE-3 trial protocol to increase the sample size from 500 participants to up to 600 participants. The primary goal of the amendment is to help ensure that the trial will have the appropriate number of disease progression events.

• The Company expects to complete enrollment of the Phase 3 ELAINE-3 clinical trial in the fourth quarter of 2026 and to have topline data in the second half of 2027.

• Independent researchers at Virginia Commonwealth University’s Massey Comprehensive Cancer Center presented nonclinical data on lasofoxifene and its potential bone protective role in metastatic breast cancer at the American Association for Cancer Research Annual Meeting 2026 (AACR26), which was consistent with LeonaBio’s data.

• The results showed lasofoxifene protected against hormone withdrawal-induced bone loss and maintained a robust anti-tumor response in primary and metastatic animal models of ER+ breast cancer. The lasofoxifene studied by the researchers was obtained from an independent s

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EX-99.1

LeonaBio Reports Full Year 2025 Financial Results and Provides Business Update

Acquired License to Phase 3 Lasofoxifene Development Program of Novel Selective Estrogen Receptor Modulator (SERM), a Potential Multi-Billion Dollar Opportunity as Treatment Option for Breast Cancer Patients with ESR1-Mutations

Received Gross Proceeds of $90 Million in Private Placement Financing of Common Stock and Warrants with Cash-Exercisable Warrants Potentially Providing up to an Additional $146 Million to Support Development of Lasofoxifene Through Key Clinical and Regulatory Milestones

Expect to Complete Enrollment of Phase 3 Clinical Trial of Lasofoxifene in ER-positive (ER+), HER2-negative, ESR1-mutated Metastatic Breast Cancer in 4Q 2026 with Topline Data Anticipated in 2H 2027

On-track to Initiate Phase 2 Proof-of-Concept Study of ATH-1105 in ALS patients in 2H 2026

BOTHELL, Wash., March 26, 2025 – LeonaBio, Inc. (NASDAQ: LONA), a clinical-stage biopharmaceutical company dedicated to the development of novel therapeutics for diseases with high unmet medical needs, today reported financial results for the year ended December 31, 2025, and provided recent pipeline and business updates.

“2025 was a truly transformational year for LeonaBio. With our license for lasofoxifene, we added a late-stage drug candidate that has the potential to become the endocrine therapy of choice in the multi-billion-dollar second line metastatic breast cancer setting” stated Mark Litton, Ph.D., President and Chief Executive Officer of LeonaBio. “Coupled with our successful $90 million fundraise with the potential for $146 million in additional capital available through warrant exercises, we enter 2026 with the financial resources needed to advance both our oncology and neurodegeneration programs with confidence.”

“Our transition from Athira Pharma to LeonaBio reflects far more than a name change; it represents our evolution into a more focused, diversified, and opportunity-driven biopharmaceutical company. We now have two clinical-stage programs and an experienced team aligned around focused execution. As we look ahead to meaningful clinical milestones in 2026 — including the anticipated completion of enrollment of the Phase 3 ELAINE-3 clinical trial and initiation of patient dosing in our ATH-1105 ALS program — we are energized by what lies ahead. We are building a company that we believe has the potential to change the treatment landscape for patients who urgently need better options, and I couldn’t be more optimistic about the momentum we carry into 2026 and beyond,” concluded Dr. Litton.

Clinical Development & Pipeline Programs

Lasofoxifene – A novel, nonsteroidal selective estrogen receptor modulator (SERM) with a unique binding profile, designed to confer potent activity against both wild-type and mutant estrogen receptors, including the clinically significant ESR1 mutations commonly associated with resistance to endocrine therapy in metastatic breast cancer.

In December 2025, LeonaBio acquired an exclusive global license (excluding Asia and certain countries in the Middle East) from Sermonix Pharmaceuticals, Inc. for rights to develop and commercialize lasofoxifene.

• Lasofoxifene is being advanced in a Phase 3 clinical trial (NCT05696626) in combination with abemaciclib, a CDK4/6 inhibitor, as a targeted therapy for estrogen receptor-positive (ER+), HER2-negative, ESR1-mutated metastatic breast cancer, a population with limited treatment options following progression on aromatase inhibitors and CDK4/6 inhibitors. The primary endpoint of the study is statistically significant improvement in progression free survival (PFS) as determined by blinded, independent central review (BICR). The ongoing Phase 3 trial aims to establish a new standard of care for this genetically defined patient group.

• LeonaBio is amending the ELAINE-3 trial protocol to increase the sample size from 500 participants to up to 600 participants. The primary goal of the amendment is to help ensure that the trial will have the appropriate number of disease progression events. The Company expects to complete enrollment of the Phase 3 ELAINE-3 clinical trial in the fourth quarter of 2026 and to have topline data in the second half of 2027.

• Lasofoxifene was previously evaluated in two Phase 2 studies in patients with ER+, HER2-negative locally advanced or metastatic breast cancer expressing an ESR1 mutation, ELAINE-1 and ELAINE-2

• ELAINE-1, an open-label, randomized trial comparing lasofoxifene to fulvestrant, showed improved outcomes for lasofoxifene as a potential monotherapy. Although the trial was not powered, results included longer median progression-free survival (5.6 vs. 3.7 months), higher objective response rates (13.3% vs. 2.9%) and a durable complete response lasting more than 2.5 years. The treatment was well-tolerated with patients reporting quality-of-life benefits.

• ELAINE-2, an open-label st