IFNA2 and neoplasm: The fact that production of serum antibodies to IFNα2b did not appear to affect tumor response in this study could be because antibody concentration is not related to treatment outcome in equine PSCC, or because the number of horses in this study is insufficient to demonstrate a difference between responders (n = 4 horses, 5 tumors) and non-responders (n = 7 horses, 7 tumors).