ABBV-706, a SEZ6-targeting antibody-drug conjugate, began first-in-human evaluation in patients with advanced solid tumors. The clinical update is logged in a Journal of Clinical Oncology supplement entry for an early dose-escalation setting. SEZ6 is positioned as a seizure-related homolog protein target, and the ADC format signals a continued push toward cell-surface biomarkers for selective delivery of cytotoxic payloads. Early-phase READOUTS typically emphasize safety, tolerability, and pharmacokinetics before efficacy signals. This study will be watched for dose-limiting toxicities and target engagement readouts that can determine whether the program advances into expansion cohorts.