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 described in the study by 1, the T staging specifically describes the depth of tumor invasion through the layers of the bowel wall. The key points to consider are:
- T1 lesions are confined to the submucosa
- T2 lesions invade into but not through the muscularis propria
- T3 lesions extend 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 staging is important for determining prognosis and treatment planning, as deeper invasion (higher T stage) generally correlates with worse outcomes and may necessitate more aggressive treatment approaches including wider surgical margins and consideration of adjuvant therapy, as noted in the study by 1. The correct classification of the tumor is crucial for guiding treatment decisions and predicting patient outcomes, and the TNM staging system provides a standardized framework for this classification, as outlined in the study by 1.
From the Research
Colorectal 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.
- 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 (≤1 mm), T3b (>1−15 mm), and T3c (>15 mm) based on the depth of invasion beyond the outer border of the muscularis propria 2.
- T1 lesions are typically defined as tumors that invade the submucosa, while T2 lesions invade the muscularis propria but not the subserosa 3, 4.
- T4 lesions are defined as tumors that invade the visceral peritoneum or other organs 5.
Depth of Invasion and Prognosis
- The depth of invasion beyond the outer border of the muscularis propria into the subserosa or nonperitonealized pericolic tissue is an important prognostic factor in colorectal cancer 2.
- The 5-year distant metastasis rate increases significantly with increasing depth of invasion, from 5.7% for pT3a to 37.2% for pT3d 2.
- The 5-year disease-free survival rate also decreases significantly with increasing depth of invasion, from 77.4% for pT3a to 50.1% for pT3d 2.
Answer to the Question
- Based on the evidence, a colorectal tumor that invades through the muscularis propria into the subserosa is a T3 lesion.
- The correct answer is (c) T3 lesion.