Study of A166 in Patients With Relapsed/Refractory Cancers Expressing HER2 Antigen or Having Amplified HER2 Gene

This is an open-label, Phase I-II, first-in-human (FIH) study for A166 as monotherapy in HER2-expressing patients who progressed on or did not respond to available standard therapies. Patients enrolled in this Phase III study must have documented HER2 positivity defined as positive on in situ hybridization (ISH) or next-generation sequencing (NGS) or HER2 expression, defined as at least 1+ by validated immunohistochemistry (IHC) test. The patient must be, in the judgment of the investigator, an appropriate candidate for experimental therapy after available standard therapies have ceased to provide clinical benefit for their disease. Patients will receive study drug as a single IV infusion at the prescribed dose level in each treatment cycle. Cycles will continue until disease progression or unacceptable toxicity. The study is divided into 2 parts (Phase I and Phase II).