Metrics For Measuring Tumor Burden: A Comparison Of Unidimensional And Volumetric Measurements

e13596 Background: Response Evaluation Criteria In Solid Tumors (RECIST) is widely used to evaluate the efficacy of anticancer therapies. However, relying upon a unidimensional length to approximate change in tumor burden may be biased. The purpose of this study was to compare tumor responses/changes assessed by volumetric and RECIST unidimensional measurements. Methods: CT scans of chest, abdomen and pelvis were acquired at 5mm slice thickness as per study protocol, from 49 patients enrolled in early phase oncology trials. Baseline and the first follow-up scans (~6 weeks) were analyzed. Tumor greatest diameter was manually measured by a radiologist and tumor volume by semi-automated computer algorithms. Results: 144 individual sites of metastatic disease were analysed, including from liver, lung and lymph nodes. As expected, the magnitude of tumor burden change was larger for volume than unidimensional measurements: 32/49 (65%) patients had an increase in tumor volume of more than 30% compared to 6/49 (12%) for unidimensional measurements. Based upon RECIST and mathematical equivalence (assuming spherical tumors) of partial response (PR) and progressive disease (PD) for volume, 9/49 (18%) patients were discordant. Out of these 9 cases, 6/9 (67%) were classified as stable disease (SD) using unidimensional measurements and PD using volume, 2/9 (22%) were classified as PD for unidimensional measurements and SD using volume, and 1/9 (11%) was classified as a PR using unidimensional measurements and SD using volume. Comparing tumor burden changes from baseline with 95% limits of agreement (derived from repeat scan reads; ECR 2011) for unidimensional measurements (-12.4, 20.4%) and volumetric measurements (-9.6, 18.0%), 20/49 (41%) patients were discordant. Out of these 20 cases, 19/20 (95%) were classified as having ‘no change’ using unidimensional and ‘change’ using volume (3/20 [15%], decrease; 16/20 [80%], increase). 1/20 (5%) patient was classified as having ‘no change’ using volume and ‘change’ (a decrease) using unidimensional measurements. Conclusions: There was some evidence to suggest that volume is more sensitive than unidimensional measurements in identifying tumor changes for individual patients.