Pearls and pitfalls of response evaluation criteria in solid tumors (RECIST) v1.1 non-target lesion assessment

Oncologic imaging is an important facet of abdominal imaging that radiologists encounter nearly every day. Many oncology clinical trials utilize response evaluation criteria in solid tumors (RECIST) version 1.1 which divides tumor sites into target and non-target lesions. Although RECIST v1.1 provides clear instructions regarding the use of imaging in clinical trials, errors in response assessment still occur using these criteria. This is especially true of response assessment with regards to non-target lesions which involve rules which are less well-defined and somewhat subjective. This pictorial essay will review RECIST v1.1 guidelines and common non-target lesion errors which can occur at baseline and follow-up response assessment.