Imaging, Diagnosis, Prognosis Variability in Assessing Treatment Response: Metastatic Colorectal Cancer as a Paradigm

Purpose: The cutoff values currently used to categorize tumor response to therapy are neither biologically based nor tailored for measurement reproducibility with contemporary imaging modalities. Sources and magnitudes of discordance in response assessment in metastatic colorectal cancer (mCRC) are unknown. Experimental Design: A subset of patients’ CT images of chest, abdomen, and pelvis were randomly chosen from a multicenter clinical trial evaluating insulin-like growth factor receptor type 1–targeted therapy inmCRC.Using Response EvaluationCriteria in Solid Tumors (RECIST), three radiologists selected target lesions and measured "uni" (maximal diameter), "bi" (product of maximal diameter and maximal perpendicular diameter), and "vol" (volume) on baseline and 6-week posttherapy scans in the following ways: (i) each radiologist independently selected andmeasured target lesions and (ii) one radiologist’s target lesions were blindly remeasured by the others. Variability in relative change of tumor measurements was analyzed using linear mixed effects models. Results: Three radiologists independently selected 138, 101, and 146metastatic target lesions in the liver, lungs, lymphnodes, andother organs (e.g., peritoneal cavity) in 29patients.Of 198 target lesions total, 33% were selected by all three, 28% by two, and 39% by one radiologist. With independent selection, the variability in relative change of tumormeasurements was 11% (uni), 19% (bi), and 22% (vol), respectively. When measuring the same lesions, the corresponding numbers were 8%, 14%, and 12%. Conclusions: The relatively low variability in change of mCRC measurements suggests that response criteria could bemodified to allowmore accurate and sensitive CT assessment of anticancer therapy efficacy. Clin Cancer Res; 20(13); 3560–8. 2014 AACR.