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Exhibit 99.1

Aptevo Provides 2Q26 Business Update and Reports Second Quarter Financial Results

Mipletamig Drives Clinical Momentum with Strong Frontline AML Data, Path Toward Phase 2

Chief Scientific Officer Appointment Strengthens Execution Across Advancing Oncology Pipeline

Non-Dilutive Grant Funding Advances APVO451 and Validates Trispecific Solid Tumor Strategy

Strategic Niowave Collaboration Opens a New Radiopharmaceutical Therapeutic Development Opportunity

SEATTLE, WA – August 14, 2026 – Aptevo Therapeutics Inc. (Nasdaq: APVO), a clinical-stage biotechnology company developing novel immuno-oncology therapeutics based on its proprietary ADAPTIR™ and ADAPTIR-FLEX™ platform technologies, today reported financial results for the quarter ended June 30, 2026 and provided a business update highlighting strong clinical progress for mipletamig, strengthened scientific leadership, non-dilutive funding to advance its solid tumor trispecific pipeline and expansion into radiopharmaceutical therapeutic development through a 50/50 collaboration with Niowave.

“During the second quarter, we made important progress against the programs and initiatives we believe can create near- and long-term value for Aptevo,” said Jeff Lamothe, President and Chief Executive Officer of Aptevo. “Mipletamig continues to lead our value creation strategy, with RAINIER generating compelling frontline acute myeloid leukemia data and moving toward completion of dose optimization by year end and Phase 2 regulatory interaction early in 2027. We also strengthened our scientific leadership, secured non-dilutive funding to advance trispecific candidate APVO451, and entered a 50/50 collaboration with Niowave that gives us a cost-effective path into radiopharmaceutical therapeutics and access to isotope supply in a constrained market. Together, these achievements put us in a stronger position to advance our pipeline and pursue multiple opportunities to create shareholder value.”

Mipletamig Drives Clinical Momentum with Strong Frontline AML Data and a Path Toward Phase 2

Mipletamig remained Aptevo’s most advanced and central value driver during the quarter, with updated Phase 1b/2 RAINIER trial data continuing to show strong clinical activity in frontline acute myeloid leukemia (AML) when combined with venetoclax and azacitidine. Across 31 evaluable unfit frontline AML patients (through Cohort 5 plus four frontline patients from the completed dose expansion trial), mipletamig demonstrated an 87% clinical benefit rate and an 81% remission rate, supporting its potential to improve standard-of-care outcomes for a patient population with significant unmet need. Safety data observed to date demonstrate mipletamig’s combinability, safety and tolerability in combination with standard-of-care therapy. RAINIER has entered the final stage of dose optimization, positioning Aptevo to complete the Phase 1b RAINIER trial and select the recommended Phase 2 dose this year in anticipation of a Phase 2 regulatory interaction in 1Q27.

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Additional Outcomes of Note

• 55% of patients who achieved CR/CRi had blast reductions that reached the important measurable residual disease-negative level (MRD neg), a result that is typically associated with stronger, more durable responses

• 36% of patients with remissions had the TP53 genetic mutation, a high-risk biomarker typically associated with poor prognosis in AML and for which most treatment options frequently fail

• 6 patients treated to date have proceeded to allogeneic stem cell transplant, which represents the best possible outcome in AML treatment and is rarely achieved in the older or unfit frontline patient population

Mipletamig was designed for the way frontline AML is treated: as an added therapeutic component to standard-of-care venetoclax and azacitidine, with the goal of increasing efficacy without materially increasing toxicity burden. Its profile is supported by clinical experience across more than 120 treated patients, no cytokine release syndrome reported in frontline patients through Cohort 5 of the RAINIER trial, activity in a medically unfit frontline population and six patients bridged to transplant, the best possible outcome in the AML treatment landscape. Importantly, mipletamig is not limited to a single genetic alteration or narrow biomarker-defined subgroup, giving it potential applicability across a broader frontline AML population where tolerability, combinability and ease of integration with venetoclax and azacitidine are central to treatment decisions.

Chief Scientific Officer Appointment Strengthens Execution Across an Advancing Oncology Pipeline

Aptevo appointed Mary J. Janatpour, Ph.D., as Senior Vice President and Chief Scientific Officer, adding more than 25 years of oncology research and development leadership to support the Company’s clinical priorities, preclinical strategy and next generation multispecific pipeline. Dr. Jana

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EX-99.1

Exhibit 99.1

Aptevo Therapeutics Provides a 1Q26 Business Update; RAINIER on Track for 2026 Completion and Phase 2 Dose Selection

Mipletamig continues to perform, delivers 87% clinical benefit and 81% remission in frontline AML, with no CRS in frontline patients

Executive leadership transition complete. Jeff Lamothe appointed CEO; Marvin White assumes Executive Chair

$60 million equity line of credit enhances financial flexibility and extends access to capital through achievement of key catalysts into 2029

SEATTLE, WA – May 13, 2026 – Aptevo Therapeutics Inc. (Nasdaq: APVO), a clinical-stage biotechnology company focused on developing novel immune-oncology therapeutics based on its proprietary ADAPTIR™ and ADAPTIR-FLEX™ platform technologies, today provided a business update.

“Aptevo is entering a defining period as a company, supported by growing clinical momentum, a committed leadership team, and a pipeline with the potential to create significant long-term value,” said Jeff Lamothe, President and Chief Executive Officer of Aptevo. “Mipletamig continues to generate compelling frontline AML data, combining strong remission activity with a differentiated safety profile with the potential as an important addition to standard-of-care therapy. At the same time, we are continuing to advance our next generation of multispecific immunotherapy programs, including our emerging trispecific candidates, which are designed to address complex solid tumors through differentiated mechanisms and targeted immune modulation. We believe our ADAPTIR and ADAPTIR-FLEX platforms position Aptevo to expand into multiple high-value areas of oncology innovation. With meaningful clinical and strategic milestones ahead, financial flexibility to support execution, and increasing validation of multispecific approaches throughout the industry, we believe we are building from an increasingly strong foundation for future growth and value creation.”

RAINIER trial on track for completion and Phase 2 dose selection by year end.

• Mipletamig continues to generate strong data in frontline acute myeloid leukemia (AML) in combination with venetoclax + azacitidine. Across 31 evaluable patients (includes data through RAINIER Cohort 5, plus 4 patients from the previously completed dose expansion trial), the data has demonstrated continued efficacy, including:

• 87% clinical benefit rate* demonstrates broad anti-leukemia activity and blast reduction across response categories

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• 81% CR or CRi (remission), compared to 66.4% in the Phase 3 VIALE-A trial**

• 65% achieved CR (complete remission), compared to 37% in the Phase 3 VIALE-A trial**

• No cytokine release syndrome (CRS), a common and often dose-limiting toxicity associated with similar therapies, has been observed in frontline patients to date

The data also show that 52% of patients who achieved CR/CRi had blast reductions that reached the important measurable residual disease-negative level, a result that is typically associated with stronger, more durable responses.

As the dataset continues to expand, efficacy and safety outcomes continue to deliver favorable results, further supporting mipletamig’s potential in the frontline setting.

*Clinical benefit rate: complete remission (CR), complete remission with incomplete hematologic recovery (CRi), and partial remission (PR)

**Phase 3 VIALE-A trial evaluating venetoclax plus azacitidine in frontline intent-to-treat AML patients who were ineligible for intensive induction chemotherapy, the reported composite CR/CRi rate was 66.4%, and the CR rate was 37% (DiNardo et al., New England Journal of Medicine, 2020).

Completed Leadership Transitions; Company Poised for a Defining Year Aptevo entered 2026 with purposeful momentum, highlighted by a planned executive leadership transition designed to support the company’s next phase of growth. Jeff Lamothe was appointed President and Chief Executive Officer, while Marvin White transitioned to Executive Chair. The move reflects continuity in strategy while positioning the organization for focused execution across clinical development, capital strategy, and long-term value creation.

Q1 2026 Cash Position

Aptevo had cash and cash equivalents totaling $14.5 million as of March 31, 2026. During the first quarter of 2026, the company raised $0.9 million, net, under the company’s Standby Equity Purchase Agreements (SEPAs) with Yorkville. For additional APVO financial information and complete access to the company’s filings, click here.

Enhanced Financial Flexibility Supports Upcoming Catalysts During the quarter, Aptevo secured a $60 million SEPA, providing meaningful access to capital and extending financial flexibility as the company advances toward planned milestones. Management believes the facility better positions Aptevo to execute strategically, support ongoing development programs, and approach future opportunities from a position of greater s

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EX-99.1

Exhibit 99.1

Aptevo Provides State of the Business Report and 2025 Financial Results

Latest mipletamig data delivers 86% clinical benefit rate with no cytokine release syndrome in 28 frontline AML patients, supporting its potential to enhance standard-of-care combination therapy

Company expands CD3 pipeline and introduces first trispecific drug candidates

SEATTLE, WA – March 26, 2026 – Aptevo Therapeutics Inc. (Nasdaq: APVO), a clinical-stage biotechnology company developing novel immune-oncology therapeutics based on its proprietary ADAPTIR and ADAPTIR-FLEX platform technologies, today reported financial results for the year ended December 31, 2025 and provided a business update highlighting recent clinical progress, pipeline expansion and capital strategy.

“2025 was a year of meaningful progress across our clinical programs, pipeline strategy and capital position,” said Marvin White, President and Chief Executive Officer of Aptevo Therapeutics. “Most importantly, recently reported mipletamig data continue to demonstrate encouraging remission outcomes together with a favorable safety profile, including no cytokine release syndrome observed in frontline patients treated to date. These results support the potential for mipletamig to enhance frontline AML treatment alongside existing standard-of-care therapy.”

White continued, “During the year we also expanded our CD3 pipeline, introduced our first trispecific programs and strengthened our access to capital to support continued execution. As I transition into the role of Executive Chair and Jeff Lamothe assumes the responsibilities of President and Chief Executive Officer, I am confident in the Company’s ability to build on this momentum.”

Highlights

Aptevo entered 2026 with momentum:

• Mipletamig Clinical Performance: Mipletaming in triplet combination therapy continues to outperform standard of care ven/aza1 in unfit frontline patients with acute myeloid leukemia (AML). This further validates a differentiated safety profile, including no cytokine release syndrome in frontline patients, suggesting it is additive to the current standard of care

• Expanded CD3 portfolio: the addition of three new multispecific candidates, leveraging the Company’s proprietary application of its differentiated CRIS7-derived CD3 binding domain, including the introduction of its first two trispecific assets

o These additions emphasize the breadth and modularity of the ADAPTIR and ADAPTIR-FLEX platforms and position the Company to address a wider range of tumor targets and combination strategies across immune-oncology

• Strengthened Financial Capacity: In 2026, the Company established a $60 million equity line facility, providing additional access to capital, subject to market conditions and the Company’s

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capital deployment strategy. If fully utilized, this facility, together with current resources, is expected to support operations into 2029.

Encouraging Frontline AML Data

Updated interim results from 28 evaluable frontline AML patients2 treated with mipletamig in combination with ven/aza demonstrate an emerging clinical profile that is additive in combination with standard of care. The triplet regimen delivered an 86% clinical benefit rate, including a 79% CR/CRi (vs. 66% )1 remission rate and a 61% complete remission rate (vs.37%)1.

Among patients achieving remission, 55% reached measurable residual disease–negative status. Notably, 35% of remissions occurred in patients with TP53 mutations, a high-risk biomarker typically associated with poor prognosis.

Importantly, no cytokine release syndrome has been observed in frontline patients treated to date. Outcomes from the mipletamig triplet compare favorably with historical results reported for the ven/aza doublet and support the potential for mipletamig to enhance frontline AML therapy for older and/or unfit patients.

“Mipletamig continues to demonstrate encouraging remission outcomes together with a consistently favorable safety profile,” said Dirk Huebner, M.D., Chief Medical Officer of Aptevo Therapeutics. “The absence of cytokine release syndrome in frontline patients underscores the potential advantage of our differentiated CD3 design in combination treatment settings.”

Huebner added, “Four patients treated to date have proceeded to allogeneic stem cell transplant, representing the most favorable treatment outcome in AML and an uncommon achievement in the older and/or unfit frontline population.”

A Differentiated CD3 Platform

During 2025 Aptevo expanded its CD3 portfolio with three new multispecific candidates, including the Company’s first two trispecific drug candidates designed to address complex solid tumor microenvironments.

All programs leverage Aptevo’s proprietary CRIS-7–derived CD3 binding domain, designed to promote targeted T-cell activation while reducing systemic immune overstimulation. Clinical experience with mipletamig, now evaluated in mo