RGS nowadays also encompasses receptor-targeted applications using tracers that specifically bind to malignant cells or components of the tumour microenvironment such as somatostatin receptors (SSTR, [12, 19]), prostate specific membrane antigen (PSMA, [17, 33]), chemokine receptor 4 (CXCR4, [15, 22]), anti-carcinogenic antigen (CEA, [34, 35]), and carbonic anhydrase IX (CAIX. The gene discussed is CA9; the disease is neoplasm.