Abstract: Labeled antibodies, antibody fragments or peptides binding to soluble cytokines or cytokine receptors are used to diagnose whether a patient has cancer or an autoimmune disease. In a preferred embodiment, a radiolabelled tag that is chemically bound to a peptide, antibody, or antibody fragment specific for sTNFR-1 and/or sTNFR2 is injected into a patient with a tumor, or suspected tumor, or with any disease associated with STNF-1/STNF-2. The patient is then imaged using standard nuclear imaging equipment to detect areas or sites of concentration of the radiolabel and/or receptor/inhibitor and/or antigen. By screening for cancer by the substances it produces, using an injected antibody to that substance with a tracer attached to it, one can detect cancer at a very early stage, potentially even microscopically.