Among animal studies related to nickel carcinogenicity, Campbell (1943) reported a twofold increase in the incidence of lung cancer in rats chronically exposed to nickel (J. A. Campbell 1943), and another study found kidney tumors in rats that received nickel sulfide, which was shown to increase erythropoietin levels and increase red blood cell levels (Sunderman Jr et al. 1982; Sunderman Jr. This evidence concerns the gene EPO and lung cancer.