This prompted us to develop, in parallel, a second ErbB3-targeted agent, MM-111, that co-targets HER2 and ErbB3.41 This bispecific antibody, which comprises two scFv fragments connected by a human serum albumin linker, is designed to dock onto HER2 receptors on HER2-positive tumor cells and potently inhibit HRG/ErbB3 based on high avidity binding. Here, ERBB3 is linked to neoplasm.