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Colorectal Cancer

*Carcinoma colorectale*

For medical students2 min readUpdated 2026-10-10

Colorectal cancer is a malignant epithelial tumor affecting various parts of the large intestine. The study of its pathological anatomy involves analyzing macroscopic growth patterns, histological structures, and pathways of tumor cell dissemination. In the vast majority of cases, the morphological substrate of the neoplasm is adenocarcinoma. Special attention in oncopathology is paid to hereditary forms, such as Lynch syndrome, which are characterized by early onset and multiple lesions.

Main HistotypeAdenocarcinoma (high, moderate, or low grade of differentiation)
MetastasisMost commonly metastasizes to regional lymph nodes and the liver
Lynch SyndromeHereditary cancer of the right colon manifesting before age 40–45
Frequent FormUlcerative/cup-shaped carcinoma (mixed growth type with ulceration)

Macroscopic Growth Patterns

The macroscopic presentation of colorectal cancer is stereotyped. Pathological anatomy traditionally distinguishes three main types of neoplasm growth relative to the bowel wall and lumen:

  1. Exophytic tumors. Characterized by growth directly into the lumen of the intestinal tube. Depending on appearance, they can be plaque-like, polypoid, or bosselated.
  2. Endophytic tumors. Characterized by infiltrative growth deep into the bowel wall and frequent surface ulceration. This group includes ulcerative and diffuse-infiltrative cancer. The latter variant is particularly dangerous because it causes pronounced narrowing of the bowel lumen.
  3. Mixed form. Represents a combination of exophytic and endophytic growth types, which is invariably accompanied by ulceration. The most striking and frequently encountered representative of this group is cup-shaped (ulcerative) carcinoma.

Histological Classification

According to the International Histological Classification, the basic and most frequent morphological form of colorectal cancer is adenocarcinoma. On microtrapes (with standard hematoxylin and eosin staining), tubular adenocarcinoma is frequently diagnosed.

Adenocarcinomas are typically divided by degree of differentiation (G) into three categories:

In addition to classic adenocarcinoma, the classification includes other histological variants:

Lynch Syndrome

A special place in the incidence structure is occupied by Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC).

From the standpoint of epidemiology and genetics, this disease is traced across multiple generations of the same family. The main clinical and morphological feature is the development of a malignant process at a very young age, typically under 40–45 years.

Lynch syndrome is characterized by a specific localization: the tumor predominantly affects the right side of the large intestine. Growth features include a high frequency of multifocal (multiple) tumors.

Furthermore, the pathology rarely occurs in isolation. It is characterized by the combination of colorectal cancer with carcinomas of other localizations. This spectrum of associated tumors includes neoplasms of:

Pathways of Metastasis

Malignant epithelial tumors of the large intestine have a pronounced potential for systemic spread. Pathological anatomy distinguishes two main pathways of colorectal cancer metastasis, most frequently documented on macro- and microscopic specimens:

  1. Regional lymph nodes. This is the first barrier on the path of lymphogenic metastasis.
  2. Liver. A very common site for distant metastases. On microsections (stained with hematoxylin and eosin), complexes of atypical cells forming metastatic nodules are clearly visualized within the liver parenchyma.

Mnemonic

To quickly remember the three main macroscopic growth forms of colorectal cancer, use the acronym EES: Exophytic (grows into the bowel lumen as polyps or plaques), Endophytic (infiltrates the wall, narrowing the lumen), and Smixed (combines both types, forming a characteristic cup-like shape).

Frequently asked questions

To which organs does colorectal cancer give distant hematogenous metastases?

Distant hematogenous metastases of colorectal cancer most frequently affect the liver, and may also be detected in the adrenal glands and lungs.

  • Liver — a typical and frequent localization of metastasis via the portal venous system.
  • Adrenal glands — colorectal cancer is one of the most frequent primary tumors in metastatic involvement of the adrenals.
  • Lungs — metastases may present atypically with the formation of endobronchial submucosal nodules causing airway obstruction.
What background and precancerous conditions precede the development of colorectal cancer?

The development of colorectal cancer is preceded by chronic inflammatory bowel diseases and polyps. Main precancerous conditions include:

  • Single and multiple polyps — dysplasia foci can form in hyperplastic polyps, which carry malignant potential.
  • Ulcerative colitis — the incidence of colon cancer is significantly higher with it than in the general population.
  • Crohn's disease — associated with a high risk of cancer, although lower than in ulcerative colitis.

Important roles are also played by hereditary syndromes, such as Lynch syndrome and familial adenomatous polyposis.

By which systems are the stage and depth of invasion of colorectal cancer evaluated?

The stage and depth of invasion of colorectal cancer are evaluated using two main systems.

  • TNM system (Tumour, Nodes, Metastasis) — an international classification where the T category reflects the depth of tumor invasion through the layers of the bowel wall (from the submucosa to the visceral peritoneum and adjacent organs).
  • Dukes classification (Dukes) — a staging system distinguishing stages A through D depending on tumor spread, lymph node involvement, and the presence of distant metastases.
What sequential genetic mutations characterize the pathogenesis of sporadic colorectal cancer?

The pathogenesis of colorectal cancer involves the sequential accumulation of genetic alterations corresponding to stages of morphological progression.

  • Hyperplastic epithelium — mutations or loss of APC, MCC genes (chromosome 5q).
  • Late adenoma — K-ras gene mutation (chromosome 12q) and mutation or loss of the DCC gene (chromosome 18q).
  • Carcinoma — mutation and loss of the p53 gene (chromosome 17q).
  • Metastatic carcinoma — further accumulation of mutations and deletion of 17q.

DNA methylation abnormalities also occur at the early adenoma stage.

Which macroscopic form of colorectal cancer is most common?

Cup-shaped (ulcerative) carcinoma is most frequently diagnosed. It belongs to the mixed form because it combines features of exophytic and endophytic growth with mandatory ulceration.

Where does colorectal cancer most commonly metastasize?

Regional lymph nodes are the first to encounter tumor cells. Among internal organs, the liver is the most frequent target for metastasis.

What is the main feature of Lynch syndrome?

It is a hereditary non-polyposis cancer that predominantly affects the right colon at a young age (under 40–45 years) and is often combined with carcinomas of other organs (e.g., endometrium or pancreas).

What synonyms does mucinous adenocarcinoma have?

In pathomorphological practice, mucinous adenocarcinoma is also called mucoid, mucinous, or colloid carcinoma. All these terms describe the same histological variant.

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