Table 1.

Representative pathological response evaluation systems

Tumour type	Criteria name	Description	Category
Gastric cancer	Mandard Tumour Regression Grade (TRG) system28	•Complete regression/fibrosis with no evidence of tumour cells •Fibrosis with scattered tumour cells •Fibrosis and tumour cells with dominant fibrosis •Fibrosis and tumour cells with a dominance of tumour cells •Tumour without evidence of regression	TRG1 TRG2 TRG3 TRG4 TRG5
	Becker classification27	•Complete tumour regression (0% residual tumour) •Subtotal tumour regression (<10% in tumour bed) •Partial tumour regression (10%-50%) •Minimal or no tumour regression (>50%)	TRG1a TRG1b TRG2 TRG3
Breast cancer	Residual cancer burden (RCB)25	RCB was calculated as a continuous index combining pathologic measurements of primary tumour (size and cellularity) and nodal metastases (number and size) •pCR •Minimal RD •Moderate RD •Extensive RD	RCB 0 RCB 1 RCB 2 RCB 3
	Definition of pCR by the US FDA (https://www.fda.gov/media/83507/download)	•The absence of residual invasive cancer on haematoxylin and eosin evaluation of the complete resected breast specimen and all sampled regional lymph (i.e. ypT0/Tis ypN0 in the current AJCC staging system) •The absence of residual invasive and in situ cancer on haematoxylin and eosin evaluation of the complete resected breast specimen and all sampled regional lymph nodes (i.e. ypT0 ypN0)
NSCLC	Junker et al.35	%RVT = viable tumour/(viable tumour + stromal tissue + necrosis) •No regression or only spontaneous tumour regression •Morphological evidence of therapy-induced tumour regression with at least 10% (grade IIa) or <10% (grade IIb) vital tumour tissue •Complete tumour regression with no evidence of vital tumour tissue.	Grade I Grade IIa Grade IIb Grade III
	Pataer et al.36	%RVT = viable tumour/(viable tumour + stromal tissue + necrosis)
Melanoma (for immunotherapy)	Tetzlaff et al.32	%RVT = area of residual viable tumour/area of total assessed cross-sectional tumour bed. The definition of total tumour bed is the area of viable tumour or tumoural regression (necrosis with or without clusters/sheets of pigmented macrophages and fibrosis/fibroinflammatory stroma)
Pan-tumour (for immunotherapy)	Immune-related pathologic response (irPR)33	%RVT = total tumour area/total tumour bed area. The definition of total tumour bed area is RVT + tumour-associated stroma + necrosis + regression bed

AJCC, American Joint Committee on Cancer; NSCLC, non-small-cell lung cancer; pCR, pathological complete response; RD, residual disease; US FDA, United States Food and Drug Administration; %RVT, % residual viable tumour.