A radioconjugate composed of the cytokine interleukin-2 (IL-2) conjugated to the bifunctional chelating agent succinimidyl-6-hydrazinopyridine-3-carboxylate (HYNIC-NHS) and co-ligand tricine and labeled with the radioisotope technetium Tc 99m (99mTc-HYNIC-IL2), that can potentially be used as a diagnostic agent to detect tumor inflammation. Upon intravenous administration, IL-2 selectively binds to the IL-2 receptor (IL-2R) expressed on tumor infiltrating lymphocytes (TILs); upon internalization, the Tc99m moiety can be visualized using radioimaging, which allows the quantification of TILs expressing IL-2R. This agent detects tumor enlargement due to invasion by TILs and not tumor progression.