How does target lesion selection affect RECIST? A computer simulation study

RECIST is grounded on the assumption that target lesion selection is objective and representative of the total tumor burden's response to therapy. A computer simulation model was designed to study target lesion selection's impact on response assessment. Readers' disagreement as a function of the total number of lesions, affected organs, and lesion growth was analyzed. Disagreement aggravates when the number of lesions increases, when lesions are concentrated on few organs, and when lesion growth borders the thresholds of progressive disease and partial response. In a metastatic setting, RECIST displays a non-linear, unpredictable behavior, not reliable for response assessment due to target lesion selection variability. Including more (if not all) lesions in the quantitative analysis of tumor burden is desirable. ### Competing Interest Statement The authors have declared no competing interest.