P1-11-2 - Ideal Number of Target Lesion Per Organ to Be Measured in Metastatic Colorectal Cancer

Abstract

Background: The criterion of 2 target lesions per organ in RECIST 1.1 is an arbitrary one and has not been supported by any objective evidence. We hypothesized that measuring the single largest lesion in each organ with metastases (modified RECIST 1.1; mRECIST 1.1) might yield the same response classification as measuring 2 target lesions per organ (RECIST 1.1).Methods: We reviewed the medical records of patients with metastatic CRC who received first-line chemotherapy between January, 2004 and June, 2013 and compared tumor responses according to two criteria using computed tomography.Results: A total of 38 patients who had at least 2 target lesions in any organ according to RECIST 1.1 were included in the study. When adopting mRECIST 1.1 instead of RECIST 1.1, 18 showed an increase in the change rate of the sum of tumor measurements. The overall response rates of chemotherapy were not significantly different between two criteria (39.4% according to RECIST 1.1 and 34.2% according to mRECIST 1.1). The best tumor response showed almost perfect agreement between RECIST 1.1 and mRECIST 1.1 (k = 0.913). Only two patients (5.3%) showed disagreement of the best responses between the two criteria.Conclusion: In the response assessment of patients with metastatic CRC, mRECIST 1.1 showed a high concordance with the original RECIST 1.1.The mRECIST 1.1, with a decreased number of target lesions to be measured, may provide more convenience in clinical practice.