What is the classification of a colorectal tumor that invades through the muscularis propria into the subserosa, specifically in terms of T(n) staging (Tumor staging)?

From the Guidelines

A colorectal tumor that invades through the muscularis propria into the subserosa is classified as a T3 lesion. According to the UICC TNM staging (8th edition) classification for colon and rectal cancer, as outlined in the study by 1, T3 lesions are defined as tumors that invade the subserosa or into non-peritonealised pericolic or perirectal tissues. The TNM staging system is crucial in determining the extent of tumor invasion and guiding treatment decisions. The classification is as follows:

• T1 lesions: tumor invades submucosa
• T2 lesions: tumor invades muscularis propria
• T3 lesions: tumor invades subserosa or into non-peritonealised pericolic or perirectal tissues
• T4 lesions: tumor directly invades other organs or structures and/or perforates visceral peritoneum The correct classification of a colorectal tumor is essential for determining the prognosis and treatment plan, as the depth of tumor invasion is a critical prognostic factor in colorectal cancer, with deeper invasion generally associated with higher risk of lymph node involvement and distant metastasis, which ultimately impacts overall survival, as noted in the study by 1.

From the Research

Tumor Classification

• The TNM classification system is used to determine the prognosis of cancer patients, with the T category reflecting the depth of tumor invasion 2, 3.
• A tumor that invades through the muscularis propria into the subserosa is classified as T3 2.
• The T3 category can be further subdivided into T3a, T3b, and T3c based on the depth of invasion beyond the outer border of the muscularis propria 2.
• T1 and T2 lesions are defined by invasion into the submucosa and muscularis propria, respectively, but not into the subserosa 4, 5, 6.
• T4 lesions are defined by invasion into other organs or structures 2, 3.

Depth of Invasion

• The depth of invasion is a critical factor in determining the prognosis of colorectal cancer patients 2, 3, 4, 5.
• Accurate distinction between deep muscularis propria invasion and subserosal invasion is essential for accurate staging and patient management 4.
• Immunohistochemical staining using smoothelin and caldesmon can help distinguish between muscularis propria and desmoplasia 4.

Answer to the Question

• Based on the evidence, a colorectal tumor that invades through the muscularis propria into the subserosa is a T3 lesion 2.
• The correct answer is (c) T3 lesion.