Exhibit 99.1

UNAUDITED PRO FORMA CONDENSED CONSOLIDATED FINANCIAL INFORMATION

On February 28, 2020, Aptevo Therapeutics Inc. (“Aptevo” or the “Company”) entered into an LLC Purchase Agreement (the “Purchase Agreement”) with Medexus Pharma, Inc. (“Medexus”), pursuant to which Aptevo sold all of the issued and outstanding limited liability company interests of Aptevo BioTherapeutics LLC (“Aptevo BioT”), a wholly owned subsidiary of Aptevo (the “Sale”). On the same date, the closing under the Purchase Agreement occurred. As a result of the Sale, Medexus acquired IXINITY (coagulation factor IX (recombinant)), a third-generation recombinant human coagulation factor IX marketed in the United States for the control and prevention of bleeding episodes and for perioperative management in adults and children 12 years of age or older with hemophilia B (the “IXINITY Business”).

As consideration for the Sale, at closing Aptevo received an amount equal to thirty million dollars ($30 million) in cash, subject to certain customary adjustments in respect of Aptevo’s estimates of cash, indebtedness, working capital and transaction expenses of Aptevo BioT as of the closing (the “Closing Consideration”). Such Closing Consideration will be subject to a final post-closing adjustment pursuant to the terms of the Purchase Agreement. Medexus deposited nine hundred and twelve thousand five hundred dollars ($912,500) with an escrow agent (i) to fund potential payment obligations of Apevo with respect to the final post-closing adjustment and (ii) to fund potential post-closing indemnification obligations of Aptevo. Aptevo may also earn milestone and deferred payments from Medexus in the future.

The unaudited pro forma condensed consolidated balance sheet as of September 30, 2019, gives effect to the disposition of the IXINITY Business as if it had occurred on September 30, 2019. The unaudited pro forma condensed consolidated statements of operations for the nine months ended September 30, 2019 and the year ended December 31, 2018 each give effect to the disposition of the IXINITY Business as if it had occurred on January 1, 2018. The unaudited pro forma condensed consolidated financial statements have been prepared in accordance with Rule 8-05 of Regulation S-X. Assumptions and estimates underlying the pro forma adjustments are described in the accompanying notes, which should be read in conjunction with the unaudited pro forma condensed consolidated financial statements. In the Company’s opinion, all adjustments that are necessary to present fairly the pro forma information have been made.

The unaudited pro forma condensed consolidated statements do not purport to represent what the Company’s financial position or results of operations would have been had the disposition of the IXINITY Business actually occurred on the dates indicated above, nor are they indicative of future financial position or results of operations. These unaudited pro forma condensed consolidated financial statements should be read in conjunction with the Company’s historical condensed consolidated financial statements and related notes for the periods presented.

This unaudited pro forma condensed combined financial information has been prepared for illustrative purposes only and is based on assumptions and estimates considered appropriate by Aptevo management; however, they are not necessarily indicative of what results of operations actually would have been assuming the sale to Medexus had been consummated as of the dates indicated, nor do they purport to represent Aptevo consolidated results of operations for future periods. The unaudited pro forma condensed financial information does not reflect any cost savings that may be realized. Actual adjustments may differ from the amounts reflected in the unaudited pro forma condensed combined financial statements and the differences may be material.

The historical financial information has been adjusted to give effect to matters that are (i) directly attributable to the sale of the IXINITY Business, (ii) factually supportable and (iii) with respect to the statement of operations, expected to have a continuing impact on the operating results of Aptevo.

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Aptevo Therapeutics Inc.

UNAUDITED PRO FORMA CONDENSED CONSOLIDATED BALANCE SHEET

As of September 30, 2019

(in thousands, except share and per share amounts)

See accompanying notes to unaudited pro forma condensed consolidated financial information

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Aptevo Therapeutics Inc.

UNAUDITED PRO FORMA CONDENSED CONSOLIDATED STATEMENTS OF

OPERATIONS

For the Nine Months Ended September 30, 2019

(in thousands, except share and per share amounts)

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Aptevo Therapeutics Inc.

UNAUDITED PRO FORMA CONDENSED CONSOLIDATED STATEMENTS OF

OPERATIONS

For the Year Ended December 31, 2018

(in thousands, except share and per share amounts)

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Aptevo Therapeutics Inc.

NOTES TO UNAUDITED PRO FORMA CONDENSED CONSOLIDATED FINANCIAL INFORMATION

Note 1. Basis of Presentation

The historical consolidated financial statements have been adjusted in the pro forma condensed consolidated financial statements to give effect to pro forma events that are (1) directly attributable to the transaction, (2) factually supportable, and (3) with respect to the pro forma condensed consolidated statements of operations, expected to have a continuing impact on the Company.

The pro forma condensed consolidated financial statements do not necessarily reflect what the consolidated Company’s financial condition or results of operations would have been had the transaction occurred on the dates indicated. They also may not be useful in predicting the future financial condition and results of operations of the Company. The actual financial position and results of operations may differ significantly from the pro forma amounts reflected herein due to a variety of factors.

Note 2. Adjustments to the Unaudited Pro Forma Condensed Consolidated Balance Sheet

The following adjustments have been made to the accompanying unaudited pro forma condensed consolidated balance sheet as of September 30, 2019:

Note 3. Adjustments to the Unaudited Pro Forma Condensed Consolidated Statement of Operations

The following adjustments have been made to the accompanying unaudited pro forma condensed consolidated statement of operations for the nine months period ended September 30, 2019:

The following adjustments have been made to the accompanying unaudited pro forma condensed consolidated statement of operations for the year ended December 31, 2018:

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