istiratumab istiratumab istiratumab (mm-141) is an experimental monoclonal antibody for the treatment of cancer. it is a bispecific antibody targeting igf-1r and erbb3. istiratumabmonoclonal antibodytype?sourcehumantargetigf1r, erbb3clinical dataother namesmm-141atc codenoneidentifierscas number1509928-04-4chemspidernoneuniixlr461md3mkeggd10943chemical and physical dataformulac8802h13532n2392o2796s58molar mass199458.51 g·mol−1 it is in development by merrimack pharmaceuticals and was awarded orphan drug status for pancreatic cancer.