When evaluating chemotherapy and targeted therapy, a smaller tumor is considered effective treatment, a constant tumor size is considered stable disease control, and an enlarged tumor is considered ineffective treatment. However, the situation after treatment with PD-1/PD-L1 inhibitors is more complex than chemotherapy and targeted therapy, and the following 4 scenarios may occur:
① tumor shrinkage;
② no change in the size of the tumor;
③ the tumor not only did not shrink but increased in size;
④ the tumor increased in size once and then decreased in size.
According to the irRC criteria promulgated by WHO, the total tumor load, in addition to tumor size, needs to be considered when assessing the efficacy of PD-1/PD-L1 inhibitors:
① Complete disease remission is considered if all lesions disappear on two consecutive assays at intervals of not less than 4 weeks;
② Consider partial remission if the total tumor load decreases by more than 50% from baseline on two consecutive tests at intervals of not less than 4 weeks;
③ Consider stable disease if the total tumor load decreases by less than 50% or increases by less than 25% on two consecutive tests.
According to iRECIST, the presence of new lesions even after PD-1/PD-L1 inhibitor therapy does not mean that the treatment is not effective. Disease progression is assessed as an increase in total tumor load of no less than 20% compared with the lowest level, but this is a pending assessment and disease progression (more aggressive disease) must be reconfirmed to be evaluated as treatment ineffective.
Co-reviewed by: Guangdong Provincial People’s Hospital Guangdong Provincial Lung Cancer Institute Dr. Wang Zhen, Deputy Chief Physician Sun Hao