Background: Pts with metastatic epithelial tumors who progress after initial therapy have a poor prognosis; new therapeutic agents could potentially improve outcomes. Trophoblast cell surface protein 2 (TROP2) is a transmembrane glycoprotein that is over-expressed on the cell surface of many epithelial cancers representing a promising target for surface-directed therapeutic modalities. Dato-DXd is an antibody-drug conjugate consisting of a humanized anti-TROP2 IgG1 monoclonal antibody covalently linked to a highly potent topoisomerase I inhibitor payload via a stable, tumor-selective, tetrapeptide-based cleavable linker. Dato-DXd monotherapy demonstrated encouraging efficacy and safety in pts with lung and breast cancer (TROPION-PanTumor01 study; NCT03401385). Methods: The phase 2, multicenter, open-label TROPION-PanTumor03 study (NCT05489211) is exploring safety and efficacy of Dato-DXd as monotherapy and in combination with various anticancer agents (e.g. durvalumab, AZD5305, nivolumab, bevacizumab, chemotherapies) that may be active in the tumor types being evaluated. TROPION-PanTumor03 is a master trial comprising independent substudies to enable simultaneous evaluation of the recommended phase 2 dose (RP2D), safety, and preliminary efficacy of Dato-DXd across several tumor types and treatment combinations. Pts with endometrial, gastric, metastatic castration-resistant prostate (mCRPC), ovarian, and colorectal (CRC) cancer are being enrolled. Eligible pts: age ≥18 years, histologically/cytologically documented advanced or metastatic disease, ≥1 measurable target lesion (RECIST 1.1) not previously irradiated (mCRPC substudy: non-measurable bone metastatic disease permitted), and adequate bone marrow and organ function. An FFPE tumor sample must be available for all pts. Prospective selection for TROP2 expression is required in pts with CRC; in all other cohorts, TROP2 expression will be analyzed retrospectively. In all monotherapy cohorts, pts will receive Dato-DXd 6 mg/kg IV infusion Q3W; in the combination cohorts, Dato-DXd 4 or 6 mg/kg Q3W, as appropriate for each combination. Pts will receive treatment until disease progression, unacceptable toxicity, or withdrawal. Primary endpoints: objective response rate, PSA50 response (mCRPC substudy only), and safety/tolerability. Secondary endpoints: progression-free survival, duration of response, disease control rate, best % change in tumor size, pharmacokinetics, and immunogenicity (anti-drug antibodies). Exploratory endpoints incl. overall survival, pt-reported outcomes, and biomarker analysis (incl. TROP2 and PD-L1 expression, tumor mutational profiling, proteomics and ctDNA profiling). Recruitment is ongoing as of Feb 2023. ©2023 American Association for Cancer Research. Reused with permission. Clinical trial information: NCT05489211.