Table 1.

Response to treatment graded by Morphology, Attenuation, Size, and Structure (MASS) criteria*.

Response category	MASS criteria description
Favorable response	No new lesions and either of the following: (1) decrease in tumor size ≥20%; (2) ≥1 predominantly solid enhancing lesion with marked central necrosis or marked decreased attenuation
Indeterminate response	Does not fit criteria for favorable or unfavorable response
Unfavorable response	Either of the following: (1) increase in tumor size ≥20% without marked central necrosis or marked decreased attenuation; (2) new metastases, marked central fill-in, or new enhancement of a previously homogeneously hypoattenuating, nonenhancing mass

*Described by Smith et al. [23].