Figure 5. Assessment of tumor regression. Using AJCC tumor regression grading (TRG), tumors were classified into four histological tumor regression grades based on the amount of vital tumor tissue and the ratio of fibrosis as follows: TRG 0, complete regression and absence of viable cancer cells; TRG 1, presence of only small clusters or single cancer cells; TRG 2, presence of residual cancer cells but with predominant fibrosis; and TRG 3, minimal or no decrease in tumor cells or extensive residual cancer.