Table 1. Key Features in the Application of RECIST 1.1 to Retrospectively Collected Radiologic Images Performed as Part of Routine Care.

RECIST 1.1	Imaging response based on RECIST	Observed deviations from RECIST 1.1 and potential effect
Lesions are classified as measurable/nonmeasurable.	Same.	NA.
Baseline method of assessment must be followed throughout the study/observation period. Lesions on chest x-ray may be considered measurable if they are clearly defined and surrounded by aerated lung.	Baseline method of assessment might not be followed for the duration of the therapy of interest.a Chest x-rays are largely unavailable in PACS or not requested. Lesions identified on chest x-ray will be selected as nontarget lesions only.	Inconsistent anatomic coverage across baseline and follow-up assessments. Might result in false determinations of response or not evaluable time points (discordant cases were 26 of 84 and 3 of 16 in the patients with and without any inconsistent anatomic coverage respectively). Inconsistent imaging modalities. May result in suboptimal readouts (discordant cases were 12 of 32 and 17 of 68 in patients with and without inconsistent imaging respectively).
An assessment of tumor burden at baseline must be performed; target and nontarget lesions must be selected and documented. (In clinical trials in patients with NSCLC, the typical specified baseline period is within 28 days of treatment initiation).	A baseline assessment is required, target and nontarget lesions are selected and documented, but baseline window is defined as 6 weeks to allow a more comprehensive capture of scans and a larger cohort.	Could not quantify.
Response categories (complete, partial, stable disease, progressive disease) classified based on measurement thresholds for target lesions, general size assessment for nontarget lesions, and the emergence of new lesions.	Same.	NA.
Assessment time points prespecified in protocol. Outside these prespecified points, assessments are computed as unscheduled assessments.	Timing of follow-up assessments is not prespecified in protocol. No concept of unscheduled assessments was applied.	Could not quantify in our retrospective cohort, where frequency was at the discretion of the treating clinicians.
Confirmation of response (for PR, CR) mandated when response rate is a main trial endpoint, with a dedicated assessment at least 4 weeks after observing initial response.	Confirmation of response requires the availability of a subsequent documentation of response no earlier than 4 weeks from the time a CR or PR is first suspected.	Missing subsequent response confirmation time points after initial response, n = 3 (3%). Might result in misclassification as nonresponders.

Abbreviations: CR, complete response; NA, not applicable; NSCLC, non–small cell lung cancer; PR, partial response.

^a Qualifying images included computed tomographic, bone scans, positron emission tomography, and magnetic resonance imaging, regardless of contrast dye administration.