Abstract

3034 Background: YL202/BNT326 is a novel ADC consisting of an anti-HER3 IgG1 monoclonal antibody linked to 8 molecules of YL0010014, a novel topoisomerase I inhibitor, via a tripeptide linker. We report preliminary safety and efficacy results from a phase I trial of YL202/BNT326. Methods: This multinational trial is recruiting patients (pts) with locally advanced/metastatic non-small cell lung cancer (NSCLC) with an EGFR-activating mutation who were previously treated with 3rd generation TKI and platinum-based chemotherapy, and pts with unresectable, locally advanced or metastatic, HR-positive and HER2-negative (IHC 0,1+,2+/ISH-) breast cancer (BC) who were previously treated with CDK4/6 inhibitor and at least one line of chemotherapy. YL202/BNT326 was given at 6 dose levels (DLs, Q3W, iv) in a BOIN dose escalation (D-ESC) scheme, followed by cohort backfill(BF) at selected doses. Primary endpoints are safety and tolerability (dose-limiting toxicities [DLTs] and adverse events [AEs]). Secondary endpoints include pharmacokinetics [PK] and efficacy per RECIST v1.1(ORR, DCR, BOR). Results: At data cutoff (4 Feb 2024), 52 pts were enrolled in D-ESC and BF (39 NSCLC, 13 BC). One DLT (grade 3 febrile neutropenia) occurred during D-ESC at the highest dose. Most common TRAEs (>20%, all grade / ≥ G3) were anemia (71%/20%), white blood cell count decreased (67%/31%), neutrophil count decreased (63%/29%), nausea (52%/0%), decreased appetite (42%/4%), lymphocyte count decreased (37%/23%), platelet count decreased (37%/10%), vomiting (37%/0%), dry mouth (25%/0%), fatigue (25%/0%), stomatitis (23%/2%), alopecia (21%/0%). Interstitial pneumonia occurred in 1 (2%) pt after COVID-19 infection. PK exposure was increased through dose escalation, with low systemic exposure of payload and no accumulation of YL202/BTN326 upon repeated administration. In 46 pts with at least 1 tumor assessment were evaluable for efficacy. Of the non-evaluable pts, 5 are on treatment pending first tumor assessment and 1 discontinued treatment prior to first assessment. In DL3 to DL5 dose range, ORR was 41.0% (95%CI, 25.6, 57.9), DCR was 94.9% (95%CI, 82.7, 99.4) across all tumor types; and the ORR in BC pts was 54.5% (95%CI, 23.4, 83.3), DCR was 100% (95%CI, 71.5, 100.0). Conclusions: YL202/BNT326 demonstrated encouraging efficacy in heavily pretreated locally advanced/ metastatic NSCLC and BC. The safety profile showed adequate safety and tolerability. Clinical trial information: NCT05653752 . [Table: see text]