radioactive components hinder repetitive imaging and tracers are relatively difficult to generate and expensive. Optical imaging could be a valuable tool for treatment monitoring at the molecular level. Optical molecular imaging is not yet available as a routine clinical modality; however, optical breast imaging devices using diffuse nearinfrared light are currently under evaluation Wee1 in clinical studies . The breast is an accessible target organ for diffuse optical imaging because light can penetrate deep enough into the tissue without having to pass through other highly absorbing or scattering tissues . Optical imaging is widely used in the preclinical setting, and new molecular imaging agents, specifically targeting cancerassociated molecules, are rapidly being developed .
The major advantages of optical imaging are that it uses no ionizing radiation and that the optical imaging probes are much less expensive and easier to generate than are PET tracers. However, Cladribine optical signal quantification is challenging and more complex than in PET imaging. We established a preclinical model to study the feasibility of optical imaging as a molecular imaging tool for treatment monitoring. If signal quantification is accurate enough to measure known treatment effects, optical imaging of putative drug targets can play a key role in highthroughput screening and testing of new drugs in preclinical models, an important application area that may help to streamline and speed up the drug development process. In addition, optical imaging has great potential to be used in clinical studies for the evaluation of drug treatment.
For instance, in the neoadjuvant setting, optical imaging could be used to verify whether the tumor responds to the targeted therapy. Optical imaging could serve as a surrogate endpoint for the evaluation eukaryotic of response to treatment at a very early stage and could obviate the need to wait for the RECIST criteria at a later stage. Measuring the response to treatment is very important in the clinical setting. Not all tumors expressing a certain target will respond to targeted therapy. For example, in a subset of highly Her2positive tumors, the response rate to trastuzumab was less than 35% . Besides antiHer2 drugs, one could also apply this strategy to other targeted treatments and for example use the individual’s response to treatment as an indicator for continued therapy after surgery .
When applied as a treatment monitoring tool in phase III clinical studies, optical imaging could be used as a secondary outcome and evaluated as a predictive biomarker for survival. We decided to use a wellestablished preclinical model with known variables to evaluate optical imaging in the application of treatment monitoring. For our xenografts, we chose Her2positive human breast cancer cell lines. Her2 overexpression is seen in approximately 25% to 30% of breast cancers and is associated with aggressive biologic behavior . Her2 has been thoroughly studied, and there are various imaging agents available that target Her2 . In our imaging experiments, we chose to use an affibody for its small size and favorable pharmacokinetic characteristics . Recently, this affibody was used to image metastatic breast cancer in humans .