Table 1.

Summary of immune-related response criteria (irRC) guidelines compared with WHO handbook and response evaluation criteria in solid tumors (RECIST 1.1).²⁴,³⁷,³⁹

Complete response (CR)
mWHO	Disappearance of all lesions in two consecutive observations ≥4 weeks apart.
RECIST 1.1	Disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm. Disappearance of all non-target lesions and normalization of tumor marker level. All lymph nodes must be non-pathological in size (<10 mm short axis).
irRC	Disappearance of all lesions in two consecutive observations ≥4 weeks apart.
Partial response (PR)
mWHO	≥50% decrease in the sum of the products of the two largest perpendicular diameters (SPD) of all index lesions vs. baseline in two observations at least 4 weeks apart, in absence of new lesions or unequivocal progression of non-index lesions.
RECIST 1.1	At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters.
irRC	≥50% decrease in tumor burden vs. baseline in two observations at least 4 weeks apart.
Stable disease (SD)
mWHO	50% decrease in SPD vs. baseline cannot be established nor 25% increase vs. nadir, in absence of new lesions or unequivocal progression of non-index lesions.
RECIST 1.1	Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study. Persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits.
irRC	50% decrease in tumor burden vs. baseline cannot be established nor 25% increase vs. nadir.
Progressive disease (PD)
mWHO	At least 25% increase in SPD vs. nadir and/or unequivocal progression of non-index lesions and/or appearance of new lesions (at any single time point).
RECIST 1.1	At least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this includes the baseline sum if that is the smallest on study). In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of at least 5 mm. Unequivocal progression of existing non-target lesions. The appearance of one or more new lesions is also considered progression.*
irRC	At least 25% increase in tumor burden vs. nadir (at any single time point) in two consecutive observations at least 4 weeks apart.
Non-index lesions (non-measurable or over allowed number)
mWHO	Changes contribute to defining best overall response of complete or partial response and stable or progressive disease.
RECIST 1.1	Changes contribute to defining best overall response of complete or partial response and stable or progressive disease.
irRC	Contribute to defining immune-related complete response (complete disappearance required).
New measurable lesions (≥5 × 5 mm)
mWHO	Always represent progressive disease.
RECIST 1.1	Always represent progressive disease.
irRC	Incorporated in tumor burden.
New non-measurable lesions (≤5 × 5 mm, bone metastases, effusions)
mWHO	Always represent progressive disease.
RECIST 1.1	Always represent progressive disease.
irRC	Do not define progression (but preclude immune-related complete response).

Note:

^*Non-CR/non-PD is preferred over SD when assessing nontarget lesion disease.

Abbreviations: irRC, immune-related response criteria; mWHO, modified World Health Organization; RECIST, response evaluation criteria in solid tumors; SPD, sum of the products of the two largest perpendicular diameters.