Tumor assessments according to RECIST versus volumetry: Impact on early changes in tumor size in metastatic colorectal cancer (mCRC).

e14043 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 the previous findings, and evaluate the agreement between RECIST-based tumor assessments (TA) and volumetry in the quantification of early changes in tumor size. Methods: mCRC patients (pts) from the FIRE-3 trial (FOLFIRI + cetuximab vs FOLFIRI + bevacizumab) underwent routine staging using contrast-enhanced CT scans. At least 2 hepatic target lesions per pt were defined for 2 raters at baseline and measured every 8 weeks using semi-automated volumetry (Siemens Syngo Via Oncology, Siemens Healthcare) and manual measurement of the LD according to 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 with limits of agreement (LOA). Agreement be...