Response Evaluation Criteria in Solid Tumors (RECIST) 1.1: Imaging Basics

RECIST guidelines exist to standardize objective response to therapy on imaging and clinical examination. We focus here on the basics of imaging criteria. Special cases will be covered in a later post.

Baseline assessment

• A tumor lesion or soft tissue component of a bony lesion are measurable if they are:
  • ≥ 10 mm on CT (slice thickness ≤ 5 mm).
  • ≥ 20 mm on chest radiography.
  • Lesions with cystic components are considered measurable; however, if non-cystic lesions are present in the same patient, these should be used as target lesions.
• A lymph node is pathologically enlarged and measurable if it is:
  • ≥ 15 mm in short-axis dimension on CT (slice thickness ≤ 5 mm).
• Non-measurable lesions include:
  • Small lesions (longest diameter <10 mm, pathological lymph nodes ≥ 10 to < 15 mm in short-axis dimension)
  • Blastic bone lesions
  • Leptomeningeal disease
  • Ascites
  • Pleural or pericardial effusion
  • Inflammatory breast disease
  • Lymphangitic involvement of skin or lung
  • Abdominal masses or organomegaly on physical exam not measurable by reproducible imaging techniques

The lesions should lend themselves to reproducible repeated measurements (i.e., the largest lesion is not necessarily the one that should be selected if it does not lend itself to reproducible measurement).

Measurable disease is defined by the presence of at least one measurable lesion as defined above. A maximum of five total lesions and a maximum of two lesions per organ are identified as target lesions and recorded and measured at baseline.

Overall tumor burden at baseline is then determined as the sum of the longest diameters of non-nodal lesions added to the sum of the short-axis dimension of nodal lesions (if nodal lesions are used as target lesions).

The sum at baseline will be used as a comparator for subsequent measurements. The same target lesions will be recorded and evaluated on subsequent imaging. Based on the behavior of these target lesions, objective tumor response is defined as:

• Complete Response: Disappearance of all target lesions. Pathological lymph nodes (target or non-target) reduced in short=axis diameter to < 10 mm.
• Partial Response: At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters.
• Progressive Disease: At least a 20% increase in the sum of diameters of target lesions AND an absolute increase of at least 5 mm in the sum of diameters of target lesions, taking as reference the smallest sum on prior studies (can include the baseline sum if that is the smallest). The appearance of one or more new lesions is also considered progression.
• Stable Disease: Neither sufficient shrinkage to qualify for partial response nor sufficient increase to qualify for progressive disease, taking as reference the smallest sum of diameters while on the study.

References

• Chalian H, Töre HG, Horowitz JM, Salem R, Miller FH, Yaghmai V. Radiologic Assessment of Response to Therapy: Comparison of RECIST Versions 1.1 and 1.0. Radiographics. 2011 Nov;31(7):2093-105.
• Eisenhauer EA, Therasse P, Bogaerts J, Schwartz LH, Sargent D, Ford R, Dancey J, Arbuck S, Gwyther S, Mooney M, Rubinstein L, Shankar L, Dodd L, Kaplan R, Lacombe D, Verweij J. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer. 2009 Jan;45(2):228-47.