Exhibit 99.1 APTEVO THERAPEUTICS REPORTS 1Q 2024 FINANCIAL RESULTS AND PROVIDES A BUSINESS UPDATE Heavily pre-treated breast cancer patient who achieved stable disease on study, remains on treatment for more than eleven months after entering the ALG.APV-527 Phase 1 trial with progressive disease and transitioning to higher dose with potential for greater clinical benefit, experienced no new adverse events since the transition to the higher dose level APVO436 Phase 1b/2 dose optimization trial initiation of ...