Glycoprotein NMB (gpNMB) is a transmembrane protein and tumor-associated antigen that is expressed at higher levels in certain malignancies than in normal tissues. Glembatumumab vedotin (CDX-011) is an antibody-drug conjugate consisting of a fully human IgG2 monoclonal antibody against gpNMB linked to the microtubule inhibitor monomethyl auristatin E (MMAE). By targeting and binding to cells overexpressing gpNMB, the antibody is internalized, allowing for intracellular release of the cytotoxic MMAE. A prior phase I/II trial of CDX-011 for refractory advanced breast cancer demonstrated an acceptable toxicity profile and an objective response rate (ORR) of 12% (NEJM JW Oncol Hematol Nov 2014 and J Clin Oncol 2014; 32:3619). In the subset of patients with triple-negative breast cancer (TNBC), the ORR was 20%, and progression-free survival (PFS) was 4.1 months; in TNBC patients with gpNMB-expressing tumors the ORR was 25%, and the PFS was 5.1 months. Now, investigators have conducted an industry-supported, randomized phase II trial (EMERGE) of CDX-011 versus investigator choice of chemotherapy (IC) in 124 refractory breast cancer patients with tumors overexpressing gpNMB (defined as ≥5% of malignant epithelial or stromal cells with any expression). ORR was similar overall for patients receiving CDX-011 or IC (6% and 7%, respectively) and for those with gpNMB-expressing tumors (12% for both). ORR was higher with CDX-011 versus IC in patients with ≥25% of tumor cells expressing gpNMB (30% vs. 9%) as well as in TNBC patients (18% vs. 0%) and TNBC patients with overexpression of gpNMB (40% vs. 0%). Dose reduction occurred in 25% of patients in both treatment arms. The most common CDX-011 toxicities were rash, fatigue, nausea, neutropenia, and neuropathy.
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