TNF and cancer: Iron restriction and the direct inhibitory action of cytokines on erythropoietic progenitors leads to suppression of erythropoiesis. A direct effect of pro-inflammatory cytokines [interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-alpha] on kidney cells that produce erythropoietin can cause impairment of erythropoietin synthesis [32], and erythropoietin levels are inadequately low for hemoglobin levels in cancer [33].