A radioconjugate consisting of the benzamide ligand ISO-1 labeled with the radioisotope fluorine F18 with positron-emitting radioisotope activity. Upon administration, fluorine [F18]ISO-1 binds to sigma-2 receptors, located on tumor cells, allowing visualization of sigma-2 receptor-expressing tumor cells with positron emission tomography (PET). Sigma-2 receptors, expressed in a variety of normal healthy tissues such as liver, kidneys, endocrine glands, and in the central nervous system, may be overexpressed in tumor cells.