Tumor response assessment by the single-lesion measurement per organ in small cell lung cancer.

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Background: The criterion of two target lesions per organ in the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 is an arbitrary one, being supported by no objective evidence. The optimal number of target lesions per organ still needs to be investigated. We compared tumor responses using the RECIST 1.1 (measuring two target lesions per organ) and modified RECIST 1.1 (measuring the single largest lesion in each organ) in patients with small cell lung cancer (SCLC). Methods: We reviewed medical records of patients with SCLC who received first-line treatment between January 2004 and December 2014 and compared tumor responses according to the two criteria using computed tomography. Results: There were a total of 34 patients who had at least two target lesions in any organ according to the RECIST 1.1 during the study period. The differences in the percentage changes of the sum of tumor measurements between RECIST 1.1 and modified RECIST 1.1 were all within 13%. Seven patients showed complete response and fourteen showed partial response according to the RECIST 1.1. The overall response rate was 61.8%. When assessing with the modified RECIST 1.1 instead of the RECIST 1.1, tumor responses showed perfect concordance between the two criteria (k=1.0). Conclusions: The modified RECIST 1.1 showed perfect agreement with the original RECIST 1.1 in the assessment of tumor response of SCLC. Our result suggests that it may be enough to measure the single largest target lesion per organ for evaluating tumor response.