T3 Lesion Classification and Clinical Significance

TNM Classification for Colorectal Cancer

The UICC TNM staging (8th edition) classification for colorectal cancer defines T3 as a tumor that invades subserosa or into non-peritonealised pericolic or perirectal tissues 1, 2, 3
T1 is defined as a tumor that invades submucosa, according to the UICC TNM staging (8th edition) classification for colorectal cancer 1
T2 is defined as a tumor that invades muscularis propria, according to the UICC TNM staging (8th edition) classification for colorectal cancer 1
T4 is defined as a tumor that directly invades other organs or structures and/or perforates visceral peritoneum, according to the UICC TNM staging (8th edition) classification for colorectal cancer 1

T3 tumors are defined by invasion through the muscularis propria into the subserosa or into non-peritonealised pericolic or perirectal tissues, without perforation of the visceral peritoneum or direct invasion of adjacent organs or structures 1, 2, 3, 4
The extent of invasion beyond the muscularis propria is an important prognostic factor for T3 tumors, with some studies suggesting a cut-off of 5 mm for higher risk 5, 6
Recent research suggests subdividing T3 into categories based on depth of invasion: T3a (≤1 mm), T3b (>1-5 mm), T3c (6-15 mm), and T3d (>15 mm) 7

Pelvic MRI is the most accurate test to define locoregional clinical staging for rectal tumors, according to the Annals of Oncology 3, 8
Endoscopic rectal ultrasound (ERUS) is more valuable for early tumors but less useful in locally advanced rectal cancer, according to the Annals of Oncology 3

Mistaking inflammatory adhesion for tumor invasion can lead to incorrect classification, and should be classified as pT1-3 depending on the anatomical depth of wall invasion 1, 4
Confusing peritoneal involvement through direct continuity (T4a) with discontinuous peritoneal deposition (M1c) can lead to incorrect classification 5, 6
Failing to recognize that tumor deposits in the subserosa without regional lymph node metastasis should be classified as N1c, not affecting the T category, according to the UICC TNM staging (8th edition) classification for colorectal cancer 1

The UICC TNM staging (8th edition) defines T3 as a tumor that invades through the muscularis propria into the subserosa or into non-peritonealised pericolic or perirectal tissues, and T4 as a tumor that directly invades other organs or structures and/or perforates the visceral peritoneum, according to the American Joint Committee on Cancer 9
T4 is further subclassified as T4a, where the tumor perforates visceral peritoneum, and T4b, where the tumor directly invades other organs or structures, as defined by the American Joint Committee on Cancer 9

Pelvic MRI is the most accurate test for locoregional clinical staging of rectal cancer, and can detect extramural vascular invasion (EMVI) and determine the distance to the circumferential resection margin (CRM), as recommended by the National Comprehensive Cancer Network 9
Endoscopic rectal ultrasound (ERUS) is more valuable for early tumors but less useful in locally advanced rectal cancer, according to the European Society of Medical Oncology 9

Mistaking inflammatory adhesion for tumor invasion can lead to incorrect classification, and tumor that is adherent to other organs macroscopically but without microscopic invasion should be classified as pT3, not T4, as stated by the National Comprehensive Cancer Network 10
Confusing tumor deposits with lymph node metastasis can also lead to incorrect classification, and a tumor nodule in the pericolorectal adipose tissue without histologic evidence of residual lymph node should be classified as N1c if it has the form and smooth contour of a lymph node, according to the National Comprehensive Cancer Network 10