The number of biomarker directed clinical trials and cancer treatments is increasing (1). This trend is driven by a series of clinical experiences that demonstrate significant improvement in clinical outcomes and progression free survival in many cancers when biomarker directed therapy is employed (2, 3). Because of these positive results, trial sponsors have increasingly mandated clinical trial designs that require biomarker testing (4). In the United States, the annual spending on clinical trials that involve targeted therapies now exceeds spending on conventional chemotherapies; and there is a resultant increased interest in maximizing information from each trials by incorporating biomarker testing (5). While many study designs permit testing of archival tissue, fresh biopsies are Cheng et al. Mandatory Biopsy Delay Clinical Trials often required for reasons such as insufficient quantity/quality as well as possible concerns about heterogeneity and evolution of the marker over time. Prior single institution studies have reported that a biopsy requirement leads to a lengthening of the screening period, however this finding has not been confirmed elsewhere....