Background: Patients with EGFR mutant NSCLC who progress on or after small molecule EGFR inhibitors have only limited treatment options. AFM24 is a tetravalent, bispecific innate cell engager that binds EGFR on solid tumor cells and CD16A on NK cells to redirect and enhance antitumor antibody-dependent cellular cytotoxicity, thus acting independently of the EGFR downstream signaling pathway and EGFR expression levels. The Phase 1 dose escalation phase of the presented study (NCT04259450) established the recommended Phase 2 dose of AFM24 monotherapy at 480 mg based on tolerability, receptor occupancy, and pharmacokinetics (PK). Correlative science data revealed an activation and enrichment of immune cells in the tumor microenvironment. Methods: The Phase 2a expansion phase is evaluating 480 mg AFM24 in patients with EGFR mutant NSCLC, relapsed or refractory to ≥1 prior lines of therapy; EGFR-positivity is defined as positive staining for EGFR in ≥1% of tumor cells per local immunohistochemistry assay. The study follows Simon’s two-stage design. The primary endpoint is overall response rate per local RECIST v1.1; secondary endpoints include safety, PK, and immunogenicity. Efficacy per iRECIST is an exploratory endpoint. AFM24 is administered intravenously once weekly in a 28-day cycle. Tumor assessments are performed at initial screening, cycles 2, 4, 6, 8, and every 3 cycles thereafter. Results: As of December 2022, 14 patients (median [range] age 55 [37–82]; 12 male; 11 Asian, 3 White) were enrolled; the median number of prior therapies was 2.5 (1–12). Median treatment duration with AFM24 was 6.7 weeks (1.0–26.1). Best objective response in 10 evaluable patients was confirmed partial response in 1 patient (change from baseline –45%); 4 patients exhibited stable disease, 1 was confirmed. Tumor shrinkage occurred in 2 patients with stable disease (–6%, –18%). The tumor control rate was 50%. Treatment-related adverse events (TRAEs) were reported in 13 patients; infusion related reactions (IRRs, 12), dermatitis acneiform, neutrophil count decreased, decreased appetite, and myalgia (2 each) were most common. Grade ≥3 TRAEs occurred in 4 patients and included decreased neutrophil count (2), lymphopenia, and IRR (1 each). Grade 5 pneumonitis was observed in 1 patient with disease progression and multiple comorbidities; relation to AFM24 could not be ruled out. As of January 2023, enrollment is ongoing; results of the interim analysis will be presented. Conclusions: AFM24 demonstrated clinical activity and acceptable safety in heavily pretreated patients with EGFR mutant NSCLC. The novel mechanism of action of AFM24 could add to the therapeutic options for patients with EGFR expressing tumors and is under clinical evaluation as a single agent and in combination with atezolizumab or autologous NK cells. Clinical trial information: NCT04259450.