Patritumab deruxtecan in leptomeningeal metastatic disease of solid tumors: the phase 2 TUXEDO-3 trial

Leptomeningeal metastatic disease (LMD) is a severe complication of solid cancers with poor outcomes and limited treatment options. The antibody-drug conjugate patritumab deruxtecan (HER3-DXd) demonstrated efficacy in breast and lung cancers, and HER3 is involved in central nervous system metastases, particularly in parenchymal colonization. In this study, we investigated HER3-DXd efficacy and safety in patients with LMD in cohort 3 of the TUXEDO-3 phase 2 trial. Key eligibility criteria included age ≥18 years, treatment-naive LMD or LMD progressing after radiotherapy from any solid tumor and Eastern Cooperative Oncology Group performance status of 0-2. Between January and July 2024, 20 evaluable patients (nine with type I and 11 with type II LMD) were accrued and received HER3-DXd 5.6 mg kg^-1 intravenously every 3 weeks. Main primary tumor types included breast (60%) and lung (30%) cancers. Median follow-up time was 5.4 months. The primary endpoint was met with 65.0% patients alive after 3 months. The Kaplan-Meier-estimated 3-month and 6-month overall survival rates were 69.6% and 58.9%, respectively. Overall response rate was 11.1% for intracranial, 30.8% for extracranial and 26.3% for overall lesions. Clinical benefit rate was 50.0% for intracranial, 38.5% for extracranial and 47.4% for overall lesions. Neurological symptoms and quality of life remained stable or improved during study treatment. No new neurological adverse events were observed. The most common adverse events of any grade were anemia (nine (40.9%) patients, one (4.5%) grade ≥3), nausea (seven (31.8%) patients, no grade ≥3), neutropenia (six (27.3%) patients, three (13.6%) grade ≥3), diarrhea (six (27.3%) patients, one (4.5%) grade ≥3), asthenia (six (27.3%) patients, no grade ≥3) and thrombocytopenia and headache (five (22.7%) patients, one (4.5%) grade ≥3 each). TUXEDO-3 showed clinically relevant HER3-DXd activity in patients with LMD. ClinicalTrials.gov identifier: NCT05865990 .