554P - Tumor Assessments According to Recist Versus Volumetry: Impact on Early Changes in Tumor Size in Metastatic Colorectal Cancer (MCRC)

Abstract

ABSTRACT Background We previously proposed an algorithm for reconstructing the true volume of a tumor lesion by using the longest diameter (LD) and the longest orthogonal diameter (LOD). The following analyses aimed to replicate these findings and evaluate the agreement between RECIST-based tumor assessments (TA) and volumetry in the quantification of early changes in tumor size. Material and methods mCRC patients (pts) treated with FOLFIRI-based therapy at the University Hospital of Munich underwent routine staging using contrast-enhanced CT scans. At least 2 hepatic target lesions per pt were defined by 2 raters at baseline and assessed every 8 weeks using semi-automated volumetry (Siemens Syngo Via Oncology) and manual measurement of the LD (RECIST 1.1) and the LOD. Agreement between the tumor volume algorithm and volumetry for each rater and the corresponding inter rater agreement (IA) were investigated using Bland-Altman (BA) plots. Agreement between the RECIST-based and volumetry-based relative changes was quantified by intraclass correlation (ICC) where 1.0 would indicate perfect agreement. Results 222 target lesions from 25 pts were measured at 99 TAs. BA plots indicated that the volume algorithm showed negligible constant bias for both raters (rater 1, 0.09 with p = 0.25, and rater 2 -0.05 with p = 0.41). IA with regard to the volumetry showed a smaller constant bias (-0.16 with p = 0.17) compared with the volume algorithm (-0.31 with p = 0.04). The relative change in tumor size between baseline and first TA was investigated. The ICCs for RECIST-based versus volumetry-based relative changes for the 2 raters were 0.79 and 0.62. Application to mCRC patients from the CRYSTAL (n = 1198) and OPUS (n = 337) studies showed the ICCs for RECIST-based versus volume algorithm-based relative changes to be 0.60 and 0.77. Conclusions The algorithm for estimating the tumor volume was validated as demonstrated by the negligible bias and the BA plots. The moderate ICCs for early changes in tumor size in the 25 Munich pts and those from the CRYSTAL and OPUS studies indicate clear differences between RECIST- and volume-based TAs and suggest that RECIST underestimates both tumor shrinkage and tumor growth. Disclosure R. Laubender: RPL receives travel support and research funding by Merck KGaA. U. Sartorius: The author is an employee of Merck KGaA. M. Schlichting: The author is an employee of Merck KGaA. S. Stintzing: The author receives: Honoraria and travel support from Merck Serono and Roche AG Honoraria from Amgen GmbH. A. Graser: The author declares that he is a member of the Siemens speakers' bureau and that he receives grant money from Bayer Pharma. V. Heinemann: The author declares: Honoraria (lectures) from Merck, Roche, Sanofi Honoraria (Ad Boards) from Merck, Roche, Sanofi Research support from Merck, Roche, Sanofi.