**11.12 Multivalency**

Multivalency has been reported as an advantage in radioimmunotherapy (Dearling & pedley, 2007). Conversion of monovalent antibodies into multivalent format increases their functional affinity and decreases dissociation rates for cell-surface and optimizes biodistribution

Breast Cancer: Radioimmunoscintigraphy and Radioimmunotherapy 189

In recent years, significant developments in the application of targeted imaging and therapy have taken place in nuclear medicine. This chapter suggests that optimization of radioimmunoscintigraphy and radioimmunotherapy methods is still possible and emphasizes that these technologies are continuing to progress and are close to become routine modalities in the identification of breast cancer sites and its therapy. The development of effective imaging and therapy of breast cancer relies to a great extent on the development of effective carriers and target agents that can deliver radionuclids to the cancer cells. These agents should be able to carry a large load of radionuclids and selectively deliver them to the cancer cells with high accuracy to achieve effective cancer cells death without inducing nonspecific toxicity. This means that the use of new targeting agents such as peptides and affibodies can provide promising results. Liposomes, dendrimers, micelles and nanoparticles present large families of carriers that can be exploited for delivery of radionuclids and they can be further improved to diagnose and therapy of breast cancer in the future. The research in the field of targeted imaging and therapy will help us to avoid unnecessary costs and potentially allow these new methods to be available for the majority

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High affinity restricts the localization and tumor penetration of single-chain Fv

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*Proceedings*, Part I. Vol 25, No. 18S: 1004

**12. Conclusion** 

**13. References** 

401.

2281.

681.

(Dearling & pedley, 2007). In addition, it allows the creation of bispecific antibody molecules that can target two different antigens simultaneously (Sergey et al., 2008). During the last decade, several techniques in multivalency engineering have been developed. Each of these strategies proposed to link monovalent domains and to produce multivalent antibody, obviously has some advantages in some special cases, but none of them is universal. The advantages of tumor targeting with multivalent antibody derivatives have been investigated for scFv dimers, prepared as disulfide-linked dimers of scFv (Adams et al., 1995), non-covalent diabodies (Kortt et al., 2001) and some other bi(multi)valent variants of recombinant antibody fragments (Kubetzko et al.,2006; Shahied et al., 2004; Willuda et al., 2001). In most cases, dimeric/divalent antibodies showed significant improvement of their pharmacokinetics and biodistribution over monomers (Sergey et al., 2008).
