Aptevo Therapeutics Inc. (APVO) SEC Filing 10-Q Quarterly report for the period ending Sunday, March 31, 2019

Exhibit 99.1

For Immediate Release

APTEVO THERAPEUTICS REPORTS 2018 FINANCIAL RESULTS

AND PROVIDES BUSINESS UPDATE

Achieves Record Annual IXINITY^® Net Revenue of $23.1 Million

Representing 111% Increase Over 2017

Advances APVO436 Into Phase 1/1b Clinical Trial for Treatment of

Acute Myeloid Leukemia and High-Grade Myelodysplastic Syndrome

Receives Authorization to Commence Dosing in Phase 1 Clinical Trial of APVO210;

Dosing Scheduled to Begin March 2019

Progresses Novel 4-1BB/5T4 Bispecific Antibody ALG.APV-527

Towards CTA Filing in Q4 2019

SEATTLE, WA – March 18, 2019

“Aptevo continued to make important progress in 2018 in both our pipeline and commercial programs setting up 2019 as a pivotal year for the Company,” said Marvin L. White, President and Chief Executive Officer.  “First, we continue to be pleased with the growth trajectory for IXINITY and our success onboarding new patients.  Net revenue for IXINITY in 2018 more than doubled to $23.1 million from $10.9 million in 2017.  New patient on-boarding has continued at a gratifying level thus far in 2019, and therefore we are optimistic about further momentum in our IXINITY business generally, and from the launch of new growth initiatives this year. These include: seeking a pediatric label expansion for IXINITY (as more than a third of patients with Hemophilia B in the U.S. are under the age of 12); introducing a more convenient 3,000 IU assay for patients; and finally, pursuing ex-US licensing and partnership opportunities for IXINITY.  We believe these initiatives will allow us to continue to grow our footprint for IXINITY in the U.S. and internationally.

We also reached a key milestone in 2018 – advancing our lead, next-generation ADAPTIR™ bispecific antibody candidate, APVO436, into clinical development.  We are particularly excited about this achievement as pre-clinical data for APVO436 has shown promising attributes, specifically by inducing lower levels of several key T cell cytokines compared to a competitor candidate, which have been associated with serious adverse events in clinical studies with other T-

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