The Assessment of Tumor Response by Measuring the Single Largest Lesion per Organ in Metastatic Tumors: A Pooled Analysis of Previously Reported Data

Background: The RECIST 1.1 adopted a total of five target lesions to be measured, with a maximum of two lesions per organ. To the best of our knowledge, the criterion of two target lesions per organ in the RECIST 1.1 is arbitrary and has not been supported by any objective evidence. Recently, we reported that the modified RECIST 1.1 (measuring the single largest lesion in each organ) showed a high level of concordance with the original RECIST 1.1 in patients with advanced or metastatic non-small cell lung cancer (NSCLC), gastric cancer (GC), and colorectal cancer (CRC). However, each study had a major limitation of a small number of patients. Methods: We conducted a pooled analysis using the data from the three individual studies to improve statistical power. Tumor responses were compared according to the RECIST 1.1 and modified RECIST 1.1 (mRECIST 1.1). Results: A total of 153 patients who had at least two target lesions in any organ according to the RECIST 1.1 were included in this pooled study: 64 with NSCLC, 51 with GC, and 38 with CRC. Regardless of primary sites, the number of target lesions according to the mRECIST 1.1 was significantly lower than that according to the RECIST 1.1 (P<0.001). The assessment of tumor responses showed a high concordance between the two criteria (k = 0.908). Only eight patients (5.2%) showed disagreement in the tumor response assessment between the two criteria. The overall response rates of chemotherapy were not significantly different between the two criteria (33.3% versus 33.3%, P=1.0). Conclusions: The modified RECIST 1.1 was comparable to the original RECIST 1.1 in the tumor response assessment of patients with advanced or metastatic NSCLC, GC, and CRC. Our results suggest that it may be possible to measure the single largest lesion per organ for assessing tumor response in clinical practice.