['In clinical trials, change in tumor size is used to stratify patients into response categories. The objective of the current study was to: 1) determine whether early change in the tumor size were correlated with survival in patients with advanced nonsmall cell lung cancer (NSCLC) using modified response categories from the Response Evaluation Criteria in Solid Tumors (RECIST), and 2) to determine whether there was an optimal percentage change in tumor size that could be used to define a partial response that also correlated with survival.', 'A total of 99 consecutive patients presenting for the treatment of advanced NSCLC during the year 2003 who had computed tomography (CT) scans before and after treatment available for review were included in the study. The largest target thoracic lesion was measured on CT before treatment, and again 2 months to 3 months after the initiation of treatment. Percent change in tumor size was calculated. The relation between tumor response and patient survival was investigated.', 'There was no definite relation noted between early tumor response and patient survival (P = .754). Patients who had any initial reduction in tumor size were not found to have a significantly different survival compared with patients with initial disease progression (P = .580). In addition, there was no particular percent reduction in tumor size that was found to optimally correlate with survival.'] Do early changes in tumor size in patients treated for advanced stage nonsmall cell lung cancer correlate with survival?