Table 1. Classification system for mrTRG and pTRG.

mrTRG		pTRG
Description	Grade	Grade	Description
No regression (intermediate signal intensity, same appearances as original tumour)	mrTRG 5	pTRG 0	No regression
Slight regression (little areas of low signal intensity fibrosis or mucin but mostly tumour)	mrTRG 4	pTRG 1	Dominant tumour mass with obvious fibrosis and/or vasculopathy
Moderate regression (low signal intensity fibrosis predominates but there are obvious areas of intermediate signal intensity)	mrTRG 3	pTRG 2	Dominantly fibrotic changes with few tumour cells or groups (easy to find)
Good regression (predominant low signal intensity fibrosis with no obvious residual tumour signal)	mrTRG 2	pTRG 3	Very few (difficult to find microscopically) tumour cells in fibrotic tissue with or without mucous substance
Complete regression (absence of tumour signal and barely visible treatment related scar)	mrTRG 1	pTRG 4	No tumour cells, only fibrotic mass (total regression or response)

Abbreviations: mrTRG=magnetic resonance tumour regression grade; pTRG=pathological tumour regression grade.