They are used to assess response to first-line treatment of glioblastoma (as well as lower grade astrocytoma). They divides response into 4 types based on magnetic resonance imaging (MRI) and clinical features: 1) complete response, 2) partial response, 3) stable disease, and 4) progression.
A measurable lesions is measured as follows: either computed tomography or MRI, contrast enhancing, clearly defined margins, visible on two or more axial slices (preferably <5 mm thick with 0 mm skip), maximal diameter and second perpendicular measurement at least 10 mm in size (if slice thickness <5 mm), or 2 times slice thickness (if slice thickness >5 mm), and do not measure cystic cavity. Non-measurable lesions are generally those that do not meet the criteria above. Additionally, and worthy of specific mention, is a cystic/necrotic tumour, or one with a surgical cavity. In such cases only a solid peripheral nodular component should be measured, provided it fulfills the above "measurable" criteria. The measurements are obtained from axial post contrast T1 images. The maximal diameter is obtained, and then the second diameter is obtained at right angles to the first. The product of these measurements is then used for the purpose of comparison.
Criteria for complete response: imaging (disappearance of all enhancing disease [measurable and non-measurable], sustained for at least 4 weeks, stable or improved non enhancing fluid attenuation inversion recovery [FLAIR]/T2 lesions, and no new lesions) and clinical features (no corticosteroids [physiological replacement doses allowed], and clinically stable or improved.
Criteria for partial response: imaging (50% or more decrease of all measurable enhancing lesions, sustained for at least 4 weeks, no progression of non-measurable disease, stable or improved non enhancing FLAIR/T2 lesions, and no new lesions) and clinical features (stable or reduced corticosteroids [compared to baseline], and clinically stable or improved).
Criteria for stable disease: imaging (does not qualify for complete response, partial response or progression, and stable non-enhancing FLAIR/T2 lesions) and clinical features (stable or reduced corticosteroids [compared to baseline] and clinically stable).
Criteria for progression: imaging (25% of more increase in enhancing lesions despite stable or increasing steroid dose, increase [significant] in non-enhancing T2/FLAIR lesions, not attributable to other non-tumour causes, and any new lesions) and clinical features (clinical deterioration [not attributable to other non-tumour causes and not due to steroid decrease]).
