B7-H4 Inhibitor Effective for Some Triple-Negative Breast Cancers

Cambridge, MA–based Mersana Therapeutics announced today that its B7-H4–targeted antibody–drug conjugate emilatug ledadotin (XMT-1660) elicited a complete response in 23% (six of 26) of patients with triple-negative breast cancer in a phase I trial. None of the patients, who had received a median of 4.5 prior therapies, developed grade 4 or 5 treatment-related adverse events (TRAE); the most common TRAEs were increases in liver enzymes and protein, experienced by 38% and 31% of patients, respectively. B7-H4 is a transmembrane glycoprotein expressed in low levels in normal tissues but upregulated in some solid tumors—notably cholangiocarcinoma and breast, ovarian, and endometrial cancers—and linked with a poor prognosis.