Molecular imaging of breast cancer

Breast cancer is the most common type of cancer in women. Imaging techniques play a pivotal role in breast cancer management, especially in lesion detection, treatment planning and evaluation, and prognostication. These imaging techniques have however limitations such as the use of ionizing radiation or radioactive components, limited sensitivity/specificity, and high costs, which motivates development of novel imaging strategies. Molecular imaging comprises visualization and characterization of cellular function and follow-up of molecular and/or biological processes, without perturbing these processes. By visualizing molecular alterations that accompany disease, molecular imaging holds promise to be able to better characterize disease states and extent at an earlier time, with lower required contrast differences than currently used imaging modalities. When fluorophores with a fluorescent spectrum in the near-infrared range (between 650-1000 nm) are applied, no ionizing radiation or radio-active compounds are required, while sufficient tissue penetration is preserved. Conjugation of fluorophores to molecules with affinity for tumor-cell specific processes (such as (therapeutic) monoclonal antibodies or antibody fragments) could improve contrast by increasing local dye concentration and reducing background signals. Development of a desirable molecular imaging tracer with clinical translation potential is however a challenging endeavor, as only a few have entered the clinical setting. In this thesis, we describe several steps in the translational process of molecular imaging tracers and technologies. We first investigate expression patterns of several important molecular targets that are expressed in breast cancer by systematic reviews and meta-analysis. We then identify, produce, and fluorescently label molecules (antibodies and nanobodies) that can bind to breast cancer targets (Carbonic Anhydrase IX and CD44v6) and evaluate, optimize and validate these tracers in vitro and in vivo. We then review current knowledge on registration and fusion of breast optical molecular images with currently used anatomical imaging modalities, which could facilitate optical image interpretation, and show that a clinical optical mammography system is able to visualize a fluorophore (approved for investigations in humans) in nanomolar concentrations with phantom experiments. Then, we show how appropriate patients for molecular imaging trials investigating the Human Epidermal Growth Factor Receptor 2 could be selected based on mammography and breast ultrasound imaging features. Selection of these patients before a diagnostic biopsy has been performed is important, as a biopsy could influence the molecular imaging results. Last, we present a clinical study protocol for investigation of a fluorescent monoclonal antibody directed to the key mediator of neo-angiogenesis in cancer, Vascular Endothelial Growth Factor-A. Molecular imaging could have an application at several stages of breast cancer management. The stability of fluorescent tracers allow for pre-, intra-, and postoperative visualization, with a single administered dose. We are now on the brink of evaluating novel fluorescent tracers and molecular imaging techniques in feasibility trials, and it is expected that several clinical studies applying fluorescent tracers will emerge in the near future. Randomized trials (comparing clinical work-up with or without molecular imaging) will ultimately be required to assess its additional value and role as clinically helpful tool.