Histological structure of colorectal tumors
The main morphological form of malignant lesion is adenocarcinoma (specifically, tubular adenocarcinoma is described in detail). Tumors must be classified according to their degree of differentiation (G):
- Well-differentiated;
- Moderately differentiated;
- Poorly differentiated.
The general histological classification of colorectal cancer also distinguishes rarer forms: mucinous adenocarcinoma, signet-ring cell carcinoma, squamous cell carcinoma, adenosquamous carcinoma, medullary carcinoma, and undifferentiated carcinoma. In oncomorphology, occult tumors are distinguished separately—these are neoplasms that showed no clinical manifestations and were not diagnosed in a timely manner during examination.
Staging of the tumor process
The prevalence of cancer is determined by its stage. To establish one of the 4 stages, the following criteria are used: tumor size, degree of organ wall involvement, involvement of surrounding tissues, and metastasis. For this, the international TNM classification (Tumour, Node, Metastasis — in the UICC edition) is applied:
- T — extent of the primary tumor (from T1 to T4).
- N — regional lymph node metastases (N1–N2).
- M — presence of distant metastases (M1a, M1b).
In case of cancer recurrence following prior surgical intervention, the lowercase letter "p" is added to the symbols (e.g., pT, pN, pM).
Survival by stage
| Stage (UICC/TNM) | Extent (T, N, M criteria) | Dukes | 5-year survival |
|---|---|---|---|
| Stage I | Invasion into the submucosa (T1) or muscularis propria (T2). No metastases. | A | 85%–95% |
| Stage II | Invasion beyond the muscular layer (T3), into the visceral peritoneum (T4a), or other organs (T4b). | B | 60%–80% |
| Stage III | Involvement of 1–3 lymph nodes (N1) or more than 3 lymph nodes (N2). | C | 30%–60% |
| Stage IVa | Distant metastases to 1 organ (M1a). | D | <10% |
| Stage IVb | Distant metastases to multiple organs (M1b). | D | <10% |
| Stage IVc | Peritoneal metastases (peritoneal carcinomatosis). | D | <10% |
Diagnostic imaging methods
Medical imaging methods are actively used to detect sigmoid colon cancer and polyps:
- MR colonography. On sagittal T1-weighted fat-suppressed images after contrast administration, polyps actively enhance with contrast medium.
- CT colonography (CTC). Effective for visualizing circular or semicircular lesions. The tumor causes luminal narrowing and forms the shouldered ends sign. Flat (plaque-like) cancer appears as local thickening with irregular wall contour (lobular fold thickening). A significant disadvantage of this method compared to traditional colonoscopy is the inability to obtain a biopsy.
- Traditional computed tomography. The malignancy of the process is confirmed by local bowel wall thickening (greater than 3 mm), extension of the tumor into pericolic adipose tissue, and enlargement of regional lymph nodes.
The tumor structure on CT is typically homogeneous. Heterogeneity occurs in large adenocarcinomas, mucinous tumors (which also frequently calcify), or in the event of abscess formation.
The meaning of the letters in the TNM system is easy to remember by their English equivalents: T — Tumor, N — Node, M — Metastasis.
Class and exam questions
How to differentiate flat cancer from circular cancer on CT?
Circular cancer causes luminal narrowing with the characteristic shouldered ends sign. Flat or plaque-like cancer is visualized as local thickening and wall irregularity (in the form of lobular fold thickening).
How do mucinous adenocarcinomas differ on imaging?
Primary and metastatic mucinous tumors often have a heterogeneous structure on CT and possess a pronounced tendency toward calcification.
What is the main disadvantage of CT colonography?
During CT colonography, unlike traditional endoscopic colonoscopy, it is not possible to perform tissue sampling (biopsy) for subsequent morphological confirmation of the diagnosis.
What else to study on this topic
- Features of colorectal cancer localization in Lynch syndrome
- Differential diagnosis with primary large bowel lymphoma
- Metastatic involvement of the colon in gastric cancer (intramural infiltration)
- Morphological changes and points of weakness in diverticular disease
- Pseudomyxoma peritonei and appendiceal pathologies (mucin deposition)
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