On Wednesday, Samsung Bioepis and Merck announced the U.S. launch of Ontruzant® (trastuzumab-dttb), a biosimilar to Herceptin® (trastuzumab).  Ontruzant® is indicated for the treatment of HER2-overexpressing breast cancer, and HER2-overexpressing metastatic gastric or gastroesophageal junction adenocarcinoma, and is available in both 150 mg single-dose vials and 420 mg multiple-dose vials.  According to the press release, Samsung Bioepis is responsible for preclinical and clinical development, manufacturing, and regulatory registration, while Merck is responsible for commercialization.  Ontruzant® is the fifth Herceptin® biosimilar to reach the U.S. market.