RECIST: no longer the sharpest tool in the oncology clinical trials toolbox---point.

Although "response" has been an attractive term for oncologists and patients, oncologists really want to know which therapy to start for a given patient and when to discontinue that therapy in favor of an alternative. In efficacy trials, cancer therapeutics have conventionally been assessed by endpoints that are based on the categorical Response Evaluation Criteria In Solid Tumors (RECIST) system. In this article, we make the case for a new paradigm in which therapeutics are assessed on a continuous scale by evidence of efficacy, using a variety of quantitative tools that take advantage of technologic innovations and increasing understanding of cancer biology. The new paradigm relies on randomized comparisons between investigational arms and control arms, as historical controls are unavailable or unreliable for these quantitative measures. We discuss multiple limitations of RECIST, including its overemphasis on tumor regression, concerns about the accuracy of tumor measurements and the validity of comparisons with historical controls, and its inadequacy in disease settings in which tumor measurements on cross-sectional imaging are difficult or uninformative. We discuss how the new paradigm overcomes these limitations and provides a framework for answering the key questions of the oncologist and improving patient outcomes.