IFNA4 and neoplasm: Of the IFNα subtypes tested in this study, we report a clear split between the subtypes anti-tumor activity, with IFNα4, IFNα5, and IFNα6 delaying tumor growth for over 100 days, whereas IFNα2 and IFNα9 are able to modulate the immune system to provide complete protection against tumor challenge in a proportion of mice.