Macroscopic and microscopic classification
Malignant neoplasms of the esophagus exhibit a variety of growth patterns. Macroscopic examination reveals three main forms: exophytic-polypoid cancer (growing into the organ lumen), flat ulcerated cancer (forming an ulcer defect), and infiltrative cancer (growing through the thickness of the wall).
At the microscopic level, two main forms predominate:
- Squamous cell carcinoma. This is the primary and most common form. Based on the degree of cellular differentiation, it is classified as well-differentiated, moderately differentiated, poorly differentiated, and undifferentiated. Histological variants include verrucous, spindle cell, and basaloid squamous cell carcinoma. Its preferred location is the middle and lower thirds of the esophagus, whereas it rarely occurs in the upper third. On hematoxylin and eosin staining, the microscopic picture demonstrates the presence of invasive complexes.
- Adenocarcinoma. Microscopically, this form presents as tubular-papillary carcinoma. Unlike squamous cell carcinoma, adenocarcinoma is strictly confined to the lower third of the esophagus and arises within the zone of Barrett's esophagus.
Important feature: intraorgan dissemination of metastases is extremely typical for both forms of esophageal cancer.
Etiology and morphological progression
The main triggering factor in the development of adenocarcinoma is the chronic effect of gastrointestinal reflux. The reflux of gastric contents leads to continuous chemical injury of the mucosa. The main aggressive agents are bile acids, low pH (acidic environment), the enzyme pepsin, and nitric oxide (NO).
Under the influence of these factors, the normal stratified squamous epithelium undergoes a sequential morphological transformation. This process is divided into six distinct stages:
- Normal stratified epithelium.
- Esophagitis (inflammation of the mucosa).
- Barrett's metaplasia (replacement of squamous epithelium).
- Low-grade dysplasia.
- High-grade dysplasia (severe atypia).
- Barrett's adenocarcinoma (invasive tumor).
Molecular and genetic alterations
Morphological progression is accompanied by profound changes at the molecular level. These disruptions are strictly tied to the stages of disease development.
Changes in cell function: Already at the stage of Barrett's metaplasia, cells acquire resistance to apoptosis (programmed cell death), and this property is retained thereafter. Later, at the stage of high-grade dysplasia, hyperproliferation is added.
Mutations and loss of allele heterozygosity:
- The earliest event is chromosomal instability, which is already detected at the stage of Barrett's metaplasia.
- During the transition to low-grade dysplasia, mutations appear in the DCC and CDKN2 genes. Mutations of the APC gene are also characteristic of this stage.
- A late event is the p53 gene mutation. It is associated with high-grade dysplasia and the direct transition to cancer.
Epimutations and gene overexpression: Epigenetic alterations of the CDKN2 gene are detected at the stage of low-grade dysplasia. Concurrently, there is an increase in the activity (overexpression) of various genes:
- Markers of early changes (NOS 2, COX 2, Src, Bcl-2) begin to be actively expressed during Barrett's metaplasia.
- At the stage of low-grade dysplasia, the expression of fibroblast growth factor and the enzyme telomerase increases.
- A marker of late progression is the overexpression of Rab11, characteristic of high-grade dysplasia.
Pathomorphological diagnostics
The diagnosis of esophageal cancer is based on the study of macro- and micropreparations.
When examining the macro-specimen of a resected (removed) esophagus, the pathologist visually evaluates the tumor node. In the case of adenocarcinoma, its association with the background condition—Barrett's esophagus—is clearly traceable.
For microscopic examination, the tissue is stained with the standard method using hematoxylin and eosin. Under the microscope, the physician verifies the histological picture: the presence of invasive complexes in squamous cell carcinoma or the formation of tubular-papillary structures against the background of metaplastic epithelium in adenocarcinoma.
Briefly: answers to topical questions
What pathways of metastasis are characteristic of esophageal cancer?
Esophageal cancer is characterized by intraorgan metastasis, as well as lymphogenous and hematogenous spread. In adenocarcinoma, the lymphogenous pathway predominates with involvement of regional lymph nodes, which include periesophageal, bifurcation, subcarinal, left gastric, and celiac nodes. Periesophageal cervical nodes are considered regional, whereas supraclavicular lymph nodes are regarded as metastatic. In late stages, visceral hematogenous metastases develop in the liver, lungs, bones, muscles, and adrenal glands.
- Lymphogenous metastasis (metastasis lymphogenes) — involvement of regional and supraclavicular lymph nodes.
- Hematogenous metastasis (metastasis haematogenes) — spread of the tumor to the liver, lungs, bones, muscles, and adrenal glands.
What risk factors lead to the development of squamous cell carcinoma of the esophagus?
Smoking and alcohol consumption, as well as the occurrence of the tumor against the background of esophageal strictures and burns, contribute to the development of squamous cell carcinoma of the esophagus. Sources also indicate that squamous cell carcinoma more frequently arises in the middle and lower thirds of the esophagus.
- Smoking and alcohol (tabaccum et alcohol) — factors against which squamous cell carcinoma of the esophagus more frequently arises.
- Esophageal strictures and burns (stricturae et combustiones oesophagi) — background conditions associated with the occurrence of squamous cell carcinoma of the esophagus.
What is the TNM classification of esophageal cancer?
The TNM classification of esophageal cancer includes the assessment of the extent of the primary tumor, regional lymph nodes, and distant metastases. Regional lymph nodes (N) are categorized depending on the number of affected nodes: from no involvement (N0) to involvement of seven or more nodes (N3). Distant metastases (M) are classified as the absence (M0) or presence (M1) of distant metastases.
- Regional lymph nodes (noduli lymphatici regionales) — assessment from N0 to N3 depending on the number of affected nodes.
- Distant metastases (metastases distantes) — division into categories M0 and M1.
What complications arise when esophageal cancer invades adjacent organs?
When esophageal cancer invades adjacent organs, severe life-threatening complications develop, including fistulae formation and vascular catastrophes. The spread of the tumor leads to the formation of tracheoesophageal or bronchoesophageal fistulae, which create a high risk of aspiration pneumonia. Invasion of the aortic wall, leading to massive hemorrhages, and the development of mediastinitis are also possible.
- Esophageal fistulae (fistulae oesophageae) — tracheoesophageal and bronchoesophageal fistulae.
- Aortic perforation (perforatio aortae) — massive hemorrhage upon destruction of the vascular wall.
To remember the damaging agents in reflux, use the phrase: Pepsin, Bile acids, Low pH, Nitric oxide (NO).
Class and exam questions
What factors provoke the development of esophageal adenocarcinoma?
The primary cause is gastrointestinal reflux. The mucosa is damaged by bile acids, low pH (acid), pepsin, and nitric oxide, which triggers a cascade of changes from inflammation to cancer.
What is the difference in localization between squamous cell carcinoma and adenocarcinoma?
Squamous cell carcinoma predominantly affects the middle and lower thirds of the esophagus (rarely found in the upper third). Adenocarcinoma is localized strictly in the lower third, within the zone of Barrett's esophagus.
Which genes mutate in the late stages of tumor development?
A late genetic event is the mutation of the p53 gene. It is associated with the stage of high-grade dysplasia and the direct transition into a malignant tumor.
What does adenocarcinoma look like under a microscope?
On hematoxylin and eosin staining, the microscopic picture of adenocarcinoma presents as a tubular-papillary carcinoma developing against the background of Barrett's metaplasia.
What else to study on this topic
- Histological variants of squamous cell carcinoma: verrucous, spindle cell, and basaloid.
- Mechanisms of tubular-papillary structure formation in adenocarcinoma.
- The role of NOS 2, COX 2, Src, and Bcl-2 genes at the stage of Barrett's metaplasia.
- Epigenetic alterations (epimutations) of the CDKN2 gene in low-grade dysplasia.
- Macroscopic evaluation of the resected esophagus in various tumor growth patterns.
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