Table 3.

The CAP tumor regression grading system

Grade	Proportion of residual viable tumor
0	No viable cancer cells (complete histological response)
1	Single cells or rare small groups of cancer cells (nearly complete response)
2	Residual cancer with evident tumor regression, but more than single cells or rare small groups of cancer cells (partial response)
3	Extensive residual cancer with no evident tumor regression (poor or no response)