Response Evaluation Criteria in Solid Tumours version 1.1 (RECIST 1.1) provides standardised criteria for evaluating changes in tumour burden in solid-tumour clinical trials. Since their publication in 2009, the criteria have been incorporated into the objectives and endpoints of numerous oncology clinical trials.1,2 Subsequent clarifications from the RECIST Committee have addressed recurring questions involving lesion selection, lymph node assessment, non-target disease, new lesions and the determination of progressive disease.

 Standardisation does not, however, eliminate the possibility of incorrect interpretation and mistakes. A recent comparison of routine clinical interpretations with formal RECIST 1.1 assessments found substantial disagreement in progressive disease classification, most commonly related to target lesion measurements and progression of non-target lesions.4 Such findings reinforce the need for appropriate training across the clinical trial team.