List of products in the National Drug Code with proprietary name . Trastuzumab is used to treat certain breast or stomach cancers that produce more than the normal amount of a certain substance called HER2 protein. Trastuzumab belongs to a class of medications known as monoclonal antibodies. It works by slowing or stopping the growth of cancer cells. This monograph is about the following trastuzumab products: trastuzumab, trastuzumab-anns, trastuzumab-dkst, trastuzumab-dttb, trastuzumab-pkrb, trastuzumab-qyyp.