The World Health Organization (WHO) introduced the system of International Nonproprietary Names in 1950, with the first INN list being published three years later. The stem "-mab" for monoclonal antibodies was proposed around 1990, and the current system with target and source substems was developed between 1991 and 1993. Due to the collaboration between the WHO and the United States Adopted Names Council, antibody USANs have the same structure and are largely identical to INNs. Until 2009, more than 170 monoclonal antibodies received names following this nomenclature.