Measuring tumour response: RECIST 1.1 and beyond

•. Response Evaluation Criteria in Solid Tumors (RECIST) standardises the method of response assessment within oncology clinical trials, allowing for results of different clinical trials to be compared. •. RECIST is based on anatomical measurement. •. RECIST 1.1 has revised some of the criteria requirements with respect to: target lesion number and measurement, lymph node measurement and the use of non-target lesions alone for overall response assessment. •. There remain some challenges for RECIST as biological response to treatment may not always result in a reduction in tumour size. •. There is an increasing requirement to measure functional parameters such as tumour metabolic activity, cellularity and vascularisation in order to acquire adequate data to effectively assess response. Currently these do not form part of the RECIST. The Response Evaluation Criteria in Solid Tumors (RECIST) were introduced in 2000 to provide a standardised method for assessing response to treatments to enable the results of different oncology clinical trials to be directly compared. The criteria are based solely on anatomical measurement of tumour size. The RECIST Working Group has recently updated RECIST to version 1.1. The revisions address issues that have arisen related to the use of the criteria in clinical practice. This article highlights these changes and also discusses the challenges that remain for response assessment using RECIST.