Among them, a very encouraging perspective is offered by 99mTc-labeled interleukin-2 (99mTc-HYNIC-IL2), which demonstrated feasibility for visualisation and quantification of tumour infiltrating lymphocytes in a small set of melanoma patients undergoing immunotherapy, so providing a potential non-invasive tool for the differentiation between progression and pseudoprogression [95]. Here, IL2 is linked to neoplasm.