AP2S1 and cancer: These observations have led to the development of the sigma-2 ligands as molecular probes for diagnostic imaging of solid tumours (Wheeler et al, 2000; Mach et al, 2001a; Kawamura et al, 2003), and the identification of sigma-2 receptors as a potential target for treatment of cancer (John et al, 1998; Caveliers et al, 2001).