**4. Targeted molecular imaging and therapy**

The researchers are trying to improve the methods that can decrease the dose of drugs and transfer them just to the tumor cells with high efficiency and kill the cancer cells without affecting healthy cells. The recent improvements in biology of tumor cells, have introduced new methods in diagnosis and therapy of cancer named targeted molecular imaging and therapy (Sawyers, 2004). The knowledge of the diversities between tumor and normal tissues is the key to identify novel targets for new selective diagnosis and therapeutic strategies (Gasparini et al., 2005). The aim of these methods is to deliver a drug for therapy or a contrast agent for imaging just to the tumor site or cancer cells using different technologies. In these methods, not only the dose of drugs is decreased, but also the damage to the normal tissues is decreased. On the other hand, the probability of the diagnosis and therapy is increased too. In addition, the targeting methods in comparison with other methods have fewer side effects and the patients tolerate less physical and mental hurts. Tumor markers are used for targeting cancer cells in molecular imaging and therapy methods. Tumor marker is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes or pharmacologic responses to a therapeutic intervention (Meel et al., 2010).
