Supporting such hypotheses are findings that fatigued breast cancer survivors demonstrated significantly higher elevations of cytokines including IL-1ra, TNF-α, sTNF-RII, IL-6, and neopterin than non-fatigued survivors, and circulating levels of IL-6, IL-1ra, and neopterin have been associated with fatigue in a quantitative review of cancer patients (159–162). Here, IL6 is linked to cancer.