Single-Lesion Measurement per Organ for Assessing Tumor Response in Advanced Gastric Cancer

OBJECTIVE: The criterion of two target lesions per organ in the revised Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) is an arbitrary decision. We assumed that measuring the single largest lesion per organ (modified RECIST 1.1, hereafter referred to as mRECIST 1.1) instead of two (RECIST 1.1) might be enough to assess tumor responses. METHODS: We compared tumor response using computed tomography according to the RECIST 1.1 and mRECIST 1.1 in patients with advanced gastric cancer (AGC) who received first-line chemotherapy. RESULTS: A total of 51 patients who had at least two target lesions in any organ according to the RECIST 1.1 were included in the study. The level of concordance in the tumor response between the RECIST 1.1 and mRECIST 1.1 was excellent (k = 0.904). Only 3 patients (5.9%) showed a disagreement of tumor responses between the two criteria. The overall response rate was not significantly different between the two criteria (45.1% by RECIST 1.1 vs. 49.0% by mRECIST 1.1, p = 0.692). CONCLUSION: The mRECIST 1.1 showed a high concordance with the original RECIST 1.1 in the assessment of tumor response for patients with AGC. Our result suggests that it may be possible to measure the single largest target lesion per organ for assessing tumor response in clinical practice.