From the Guidelines
A colorectal tumor that invades through the muscularis propria into the subserosa is a T3 lesion. The TNM staging system for colorectal cancer, as outlined in the 8th edition of the UICC TNM staging classification 1, provides a framework for classifying the extent of the primary tumor's invasion through the layers of the bowel wall. According to this system:
- T1 lesions are confined to the submucosa
- T2 lesions invade into but not through the muscularis propria
- T3 lesions penetrate through the muscularis propria into the subserosa or into non-peritonealized pericolic or perirectal tissues
- T4 lesions directly invade other organs or structures and/or perforate the visceral peritoneum. This classification is crucial for determining prognosis and treatment planning, as deeper invasion correlates with higher risk of lymph node involvement and distant metastasis, ultimately impacting morbidity, mortality, and quality of life. The use of high-quality imaging modalities like pelvic magnetic resonance imaging (MRI) can help accurately define locoregional clinical staging, including the T substage and distance to the circumferential resection margin (CRM), which are essential for selecting patients for appropriate preoperative management and defining the extent of surgery 1.
From the Research
Colorectal Tumor Staging
- 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 colorectal tumor that invades through the muscularis propria into the subserosa is classified as a T3 lesion, according to the TNM classification system 2.
- The T3 category is defined by a tumor that invades through the muscularis propria into pericolorectal tissues, and can be further subdivided into T3a, T3b, and T3c based on the depth of invasion beyond the outer border of the muscularis propria 2.
- In contrast, a T2 lesion is defined as a tumor that invades through the muscularis mucosae into the muscularis propria, but does not extend into the subserosa 4, 5.
- A T1 lesion is defined as a tumor that invades the submucosa, but does not extend into the muscularis propria, and a T4 lesion is defined as a tumor that invades through the visceral peritoneum or into other organs 3.
Key Characteristics of T3 Lesions
- T3 lesions are characterized by invasion through the muscularis propria into the subserosa, and can be further subdivided based on the depth of invasion 2.
- The prognosis of T3 lesions varies based on the depth of invasion, with deeper invasion associated with a poorer prognosis 2.
- Accurate distinction between T3 lesions and other stages of colorectal cancer is essential for proper staging and treatment 6.
Answer to the Question
- Based on the TNM classification system, a colorectal tumor that invades through the muscularis propria into the subserosa is a T3 lesion.
- Therefore, the correct answer is (c) T3 lesion.