Table 5.

The MSK Regression Schema. Please refer to the following video for endoscopic and MRI response assessment—https://www.youtube.com/watch?v=38rsqZvJIHg

MSK Regression Schemae
	Clinical Complete Response	Near Complete Response	Incomplete / No Response
Endoscopy	Flat, white scar Telangiectasia No ulcer No nodularity	Irregular mucosa Superficial ulceration Mild persisting erythema of the scar	Visible tumor
Digital Rectal Exam	Normalf	Smooth induration or minor mucosal irregularityf	Palpable tumor nodulesf
MRI-T2WI	Normal appearing rectal wall OR Only fibrosis (dark T2 signal) and no intermediate signal intensity at the site of tumora AND No suspicious lymph nodesb	Predominantly fibrosis at the site of tumora with punctate areas of T2 intermediate signal AND/OR No suspicious or borderline enlarged lymph nodesb	Predominantly residual tumor with T2 intermediate signal and no or minimal fibrosis at the site of tumora AND/OR Suspicious lymph nodesb AND/OR Mucin at the site of tumord
MRI-DWI	No restricted diffusionc at the site of tumora	Punctate areas of restricted diffusionc at the site of tumora	Restricted diffusionc at the site of tumora

^aSite of tumor: rectal wall, extramural vascular invasion and/or tumor deposit.

^bSuspicious lymph nodes criteria: (a) mesorectal and superior rectal nodes > 0.5 cm in the short axis; (b) internal iliac > 0.4 cm in the short axis particularly if suspicious on baseline; (c) obturator > 0.6 cm in the short axis particularly if suspicious on baseline; (c) mucin within the lymph nodes since MRI cannot distinguish cellular from acellular mucin. Additional lymph nodes should be interpreted cautiously, as there are no well-defined radiological criteria to strongly support their significance.

^cRestricted diffusion: high signal on DWI high b-value (minimum b800) and low signal on ADC map.

T2 dark through (low signal on both DWI and ADC map) and T2 shine thought (high signal on both DWI and ADC map) effects are not considered restricted diffusion.

^dMRI is unable to differentiate cellular from acellular mucin.

^eClinicians can also refer to the following website for examples of cCR, nCR, and iCR: https://nomtrial.mskcc.org/Home/Index

^fNote not all tumors can be palpated (e.g., 10-12 cm from the anal verge) and thus the endoscopic features will be paramount and take precedent for decision-making in these mid-rectal tumors along with the MRI features