Macroscopic growth patterns
The macroscopic picture of colorectal cancer is characterized by stereotypy. Pathological anatomy traditionally distinguishes three main types of neoplasm growth in relation to the bowel wall and lumen:
- Exophytic tumors. Characterized by growth directly into the lumen of the intestinal tube. Depending on their appearance, they can be plaque-like, polypoid, or coarsely nodular.
- Endophytic tumors. Distinguished by infiltrative growth deep into the bowel wall and frequent surface ulceration. This group includes ulcerative and diffuse-infiltrative carcinoma. The latter variant is particularly dangerous because it causes pronounced narrowing of the bowel lumen.
- Mixed form. Represents a combination of exophytic and endophytic growth patterns, which is inevitably accompanied by ulceration. The most prominent and frequently encountered representative of this group is ulcerative (saucer-like) carcinoma.
Histological classification
According to the International Histological Classification, the baseline and most frequent morphological form of colorectal cancer is adenocarcinoma. On microscopic slides (with standard hematoxylin and eosin staining), tubular adenocarcinoma is frequently diagnosed.
Adenocarcinomas are conventionally divided by the degree of differentiation (G) into three categories:
- Well-differentiated;
- Moderately differentiated;
- Poorly differentiated.
In addition to classical adenocarcinoma, the classification includes other histological variants:
- Mucinous adenocarcinoma. In literature, it may also be found under the synonyms: mucoid, mucinous, or colloid carcinoma.
- Signet-ring cell carcinoma.
- Undifferentiated carcinoma.
- Unclassified carcinoma.
Lynch syndrome
A special place in the incidence structure is occupied by Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer.
From the perspective of epidemiology and genetics, this disease can be 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, as a rule, before 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. A combination of colorectal cancer with carcinomas of other localizations is characteristic. This spectrum of associated tumors includes neoplasms of:
- Endometrium;
- Small intestine;
- Ovaries;
- Ureters and renal pelves;
- Pancreas.
Metastatic pathways
Malignant epithelial tumors of the large intestine possess a pronounced potential for dissemination throughout the body. Pathological anatomy distinguishes two main pathways of colorectal cancer metastasis, which are most frequently recorded on macro- and microscopic preparations:
- Regional lymph nodes. This is the first barrier on the path of lymphogenic metastasis.
- Liver. This is a very frequent localization for distant metastases. On microscopic slides (with hematoxylin and eosin staining), complexes of atypical cells forming metastatic nodules are clearly visualized in the liver tissue.
Briefly: answers to topical 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 vein system.
- Adrenal glands — colorectal cancer is one of the most frequent primary tumors in metastatic involvement of the adrenals.
- Lungs — metastases can present in an atypical form with the formation of endobronchial submucosal nodules causing airway obstruction.
Which background and precancerous diseases precede the development of colorectal cancer?
The development of colorectal cancer is preceded by chronic inflammatory bowel diseases and polyps. The main precancerous conditions include:
- Single and multiple polyps — areas of dysplasia can form in hyperplastic polyps, which carry malignant potential.
- Ulcerative colitis — the frequency of colon cancer development in this condition is significantly higher than in the general population.
- Crohn's disease — associated with a high risk of cancer, although lower than in ulcerative colitis.
Hereditary syndromes, such as Lynch syndrome and familial adenomatous polyposis, also play an important role.
By which systems are the stage and depth of invasion of colorectal cancer assessed?
The stage and depth of invasion of colorectal cancer are assessed 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 intestinal wall (from the submucosa to the visceral peritoneum and adjacent organs).
- Dukes' classification (Dukes) — a staging system distinguishing stages from A to D depending on tumor spread, lymph node involvement, and the presence of distant metastases.
Which sequential genetic mutations are characteristic of the pathogenesis of sporadic colorectal cancer?
The pathogenesis of colorectal cancer involves the sequential accumulation of genetic alterations corresponding to the 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 17q deletion.
DNA methylation disruption also occurs at the early adenoma stage.
For quick memorization of the three main macroscopic growth patterns of colorectal cancer, use the acronym EEM: Exophytic (grow into the bowel lumen as polyps or plaques), Endophytic (infiltrate the wall, narrowing the lumen), and Mixed (combine both types, forming a characteristic saucer shape).
Class and exam questions
What is the most common macroscopic form of colorectal cancer?
Ulcerative (saucer-like) carcinoma is the most frequently diagnosed. It belongs to the mixed form because it combines features of exophytic and endophytic growth with obligatory ulceration.
What is the most frequent site of metastasis for colon cancer?
The regional lymph nodes are the first to encounter tumor cells. Among internal organs, the liver becomes the most frequent target for metastases.
What is the main feature of Lynch syndrome?
This is a hereditary nonpolyposis cancer that predominantly affects the right parts of the large intestine at a young age (before 40–45 years) and is frequently combined with carcinomas of other organs (e.g., endometrium or pancreas).
What are the synonyms for mucinous adenocarcinoma?
In pathological practice, mucinous adenocarcinoma is also referred to as mucoid, gelatinous, or colloid carcinoma. All these terms describe the same histological variant.
What else to study on this topic
- Morphological differences between high-, moderate-, and low-grade adenocarcinoma
- Features of diffuse infiltrative carcinoma and mechanisms of intestinal lumen narrowing
- Multifocal tumor growth in hereditary nonpolyposis colorectal cancer
- Microscopic appearance of tubular adenocarcinoma stained with hematoxylin and eosin
- Histological specificities of signet-ring cell and undifferentiated carcinoma
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