Table 2. Three-tier system of response assessment developed for the OPRA trial.

	Complete response	Near-complete response	Incomplete response
Endoscopy	• Flat, white scar • Telangiectasia • No ulcer • No nodularity	• Irregular mucosa • Small mucosal nodules or minor mucosal abnormality • Superficial ulceration • Mild persisting erythema of the scar	• Visible tumor
Digital rectal examination	• Normal	• Smooth induration or minor mucosal abnormalities	• Palpable tumor nodules
T2W-MRI	• Normal appearing bowel wall without any fibrosis in the tumor bed • Only dark T2 signal, no intermediate T2 signal • No visible lymph nodes or very few, small (<5 mm) nodes	• Mostly dark T2 signal, some remaining intermediate signal and / or • Partial regression of lymph nodes	• More intermediate than dark T2 signal, no T2 scar and / or • No regression of lymph nodes
DW-MRI	• No visible signal on B800–B1000 and / or • Uniform, linear signal in the wall above the tumor is acceptable	• Significant regression of signal on B800–B1000	• Insignificant regression of signal on B800–B1000

Abbreviations: DW-MRI, diffusion-weighted magnetic resonance imaging; OPRA, organ preservation in rectal adenocarcinoma; T2W-MRI, T2-weighted magnetic resonance imaging.