Cancer is a leading cause of death worldwide. Fortunately an abundance of cancer drugs are becoming available; the challenge now is to select the most promising. Integrated cancer research and biomarker-driven adaptive and hypothesis-testing clinical trials are imperative. Many tumor characteristics can now be visualized simultaneously, but the necessary tracers have hardly been explored clinically. In the onQview program, we aim to create a drug development strategy based on a novel non-radioactive molecular imaging approach to guide patient-tailored selection of drugs, to measure in vivo drug and tumor behavior, and to allow dynamic treatment tuning. Our extensive (pre)clinical experience with molecular imaging and drug development is hereby merged with our unique infrastructure, including lasers, microscopes, and advanced detection systems for non-ionizing electromagnetic waves, for optical and photoacoustic imaging modalities. We will develop novel non-radioactive tracers based on HER-targeting drugs in breast and colon cancer, and use molecular imaging to track the drugs and corresponding effect sensors that visualize targeting effects. This approach will allow dynamic treatment tuning in pre-clinical (animal) experiments. We will also advance the implementation of optical and photoacoustic imaging with optimized measurement techniques and quantification strategies that will allow testing of the new tracers in breast/colon cancer models. Two tracers will be produced for human use and evaluated in clinical studies that enable visualization of drug behavior, drug targets and drug effects in relation to the HER family in breast and colon cancer.