Radiotracers for Molecular Imaging of Breast Cancer

Abstract

Breast cancer is the most prevailing malignancy among women in the world. 207,090 new cases of invasive breast cancer, along with 54,010 new cases of non-invasive types are expected to be diagnosed in women in the United States in 2010. Moreover, about 39,840 women are projected to die from this disease in the U.S in 2010. According to National Cancer Institute, the 5-year survival rate of breast cancer ranges from 23.4% in patients with stage IV to 98% in patients with stage I, highlighting the importance of early detection and diagnosis of this disease(American Cancer Society, 2010). Molecular imaging does not only serve as an essential tool in breast cancer diagnosis and staging, but also provides significant amount of information for surgical management, radiation planning, chemotherapeutic assessment, and follow-up evaluation of patients. Currently, positron emission tomography (PET), single photon emission computed tomography (SPECT), and their combinations with CT, are major functional molecular imaging modalities used in clinic. Both PET and SPECT are based on the detection of radiolabeled ligands, termed “radiotracers”, which are assumed to target tumor-specific characteristics at molecular levels. The accumulating understanding of the breast cancer molecular biology has highlighted pivotal factors that are critical for breast cancer progression, which allows researchers to select suitable targets for developing tumorspecific radiotracers. For instance, given that sustained tumor growth demands elevated glucose consumption for energy production in the lesion regions, PET radiotracer 18Flabeled glucose analog 18F-FDG has commonly been used to visualize the glucose metabolism of breast cancer cells(Buerkle & Weber, 2008). And yet, 18F-Fluoroestradiol is used to image estrogen receptor, which is highly overexpressed in a large proportion of breast tumor tissues(Jonson & Welch, 1998). Many other radiotracers have been designed to image cell proliferation, cell apoptosis, angiogenesis and hypoxia of breast tumors. Since breast cancer treatment has become more individualized in compliance with the distinct biological characteristics of tumors from each patient, the more target-specific molecular imaging radiotracers may play a key role to guide treatment selection and evaluate treatment response in the early stages. This chapter has firstly been focused on two major molecular imaging modalities, PET and SPECT, their principles, limitations, as well as the typical radionuclides applied for those