Chelate peptide is an organic compound and commonly used as a complexing agent, which have been widely used as contrast agents for cancer treatments. It can also be linked to molecules that have affinity to various structures (e.g. somatostatin receptors on neuroendocrine tumours). The generated compounds may combine with a number of radioisotopes to be used in cancer therapy and diagnosis. For example, DOTA could act as a chelator for a radionuclide. (Tyr3)-octreotate, a derivative of octreotide, can bind to somatostatin receptors that are found on the cell surfaces of a number of neuroendocrine tumours. Therefore, DOTA-(Tyr3)-Octreotate is able to direct the radioactivity into the tumour.