ARRS 2022 Abstracts

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E1937. Is It Getting Better? Comprehensive Review of RECIST 1.1 for Evaluation of Solid Tumors
Authors
  1. Parth Kumar; Department of Medicine, University of California, Irvine
  2. Thanh-Lan Bui; Department of Radiological Sciences, University of California, Irvine
  3. Justin Glavis-Bloom; Department of Radiological Sciences, University of California, Irvine
  4. Ngoc Le; Department of Radiological Sciences, University of California, Irvine
  5. Michael Nguyentat; Department of Radiology, University of Colorado
  6. David Kakish; Department of Radiological Sciences, University of California, Irvine
  7. Roozbeh Houshyar; Department of Radiological Sciences, University of California, Irvine
Background
RECIST is a disease assessment that provides a simple and pragmatic way to evaluate the activity and efficacy of new cancer therapeutics in solid tumors. The RECIST working group is comprised of representatives from the European Organization for Research and Treatment of Cancer, National Cancer Institute, and the Canadian Cancer Trials Group, and several pharmaceutical companies. The first set of guidelines was developed and published in February 2000. RECIST 1.1 is the revision that came out in 2009 to clarify the selection of target lesions, the definition of stable disease, what to do with measurable lesions not initially selected for target disease response, and the frequency of tumor evaluation, among others.

Educational Goals / Teaching Points
The purpose of this educational abstract is to review the RECIST 1.1 guidelines and teach radiology trainees and practicing radiologists how to apply these guidelines, using representative cases. By the end of this exhibit, the viewer should be able to define stable disease (SD), progressive disease (PD), complete response (CR), and partial response (PR). In addition, the viewer should be able to understand the difference between measurable and non-measurable lesions. Finally, we will discuss pitfalls and best practices for applying the RECIST 1.1 guidelines.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
RECIST 1.1 recommends contrast-enhanced CT as the modality of imaging because it is more sensitive than plain film radiography in identifying new lesions. Additionally, MRI can be used similarly to CT. Chest radiography (CXR) can be considered if the margins of the lesion are well-identified and surrounded by well-aerated lungs, but it is not the preferred imaging modality. PET can be used to assess PD or to confirm CR. Ultrasound should not be used in measurement of lesions as it is operator dependent and cannot be reproduced for independent review. CR is defined as the disappearance of all target lesions and a reduction in size of any pathological lymph nodes to < 10 mm in the short axis. PR is considered an at least 30% decrease in the sum of diameters of the target lesions from the baseline sum of diameters. PD is considered to be an at least 20% increase in the sum of diameters of target lesions from the smallest sum (baseline or interval). In addition, PD can be an absolute increase of at least 5 mm, or the appearance of one or more new lesions, including non-target lesions. SD is defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD.

Conclusion
The RECIST 1.1 guidelines serve as a standardized way of assessing tumor response to cancer therapeutics. It serves as a common language for radiologists to use when discussing the effect of existing and new cancer therapeutics. Therefore, it is essential for both radiology trainees and practicing radiologists to be familiar with these guidelines and how to apply them.