ERBB2 and neoplasm: Many receptor targets are subject to enzymatic cleavage that releases the soluble extracellular domain, e.g., CEA, HER2, CD19, and BCMA, thereby leading to variable and heterogeneous target receptor expression on tumor cells and even antigen escape.189 Multispecific antibodies with different targeting abilities are viable agents for limiting antigen escape and increasing the specificity of tumor targeting.