Window-of-opportunity trial

Window trials compare the diagnostic biopsy with the resected tumour after 2-6 weeks of drug, measuring proliferation (Ki-67 in breast cancer, the basis of POETIC and many endocrine studies), immune infiltration after checkpoint inhibitors, target engagement and early resistance signals; they use tens of patients rather than hundreds and can rank candidate drugs or combinations quickly. They cannot measure survival benefit and short exposure may miss slow effects, and delaying surgery must be justified. Neoadjuvant trials with pathological response endpoints are the longer, efficacy-oriented relative; the site's ideas include window designs for ctDNA, neural and microbiome interventions.