Window of opportunity studies: Do they fulfil our expectations?

• Window studies are trials in which a new compound is given between the diagnosis and the standard treatment.
• Window studies offer the possibility to evaluate the activity of agents in unbiased conditions, and to obtain pharmacodynamic and predictive parameters.
• The challenges are patient safety and ethics.
• Window studies for breast cancer have led to promising hypotheses that should be confirmed in larger trials.

Window of opportunity studies are trials in which patients receive one or more new compounds between their cancer diagnosis and standard treatment (mainly surgery). Patients are generally cancer treatment naïve. Tumor biopsies before and after the investigational treatment are collected for translational research. Similarly, anatomic and functional pre- and post-treatment imaging may be incorporated. Ideally, the investigational treatment is kept short to avoid delaying standard treatment.Window of opportunity trials may expedite drug development, improve our understanding of pharmacodynamic parameters, and help to identify biomarkers for better patient selection. They can, however, have major drawbacks including potential safety and logistical issues, delayed standard treatment, and a probable lack of patient benefit. By focusing on breast and head and neck cancers, in this paper we discuss the advantages, disadvantages and design of window of opportunity studies.