Histological classification (WHO, 2004)
According to the WHO histological classification, lung tumors are divided into main histological types and their variants. The following groups are distinguished:
- Squamous cell carcinoma. Includes papillary, clear cell, small cell, and basaloid variants. Examination of a micro-specimen of high-grade keratinizing squamous cell carcinoma using the immunoperoxidase method reveals a specific diagnostic feature: the presence of pancytokeratins in the cancer cells.
- Small cell carcinoma. Includes combined carcinoma, among others.
- Adenocarcinoma. Includes acinar, papillary, solid adenocarcinoma with mucin production, and a mixed subtype. Bronchioloalveolar carcinoma is distinguished separately, with variants including non-mucinous, mucinous, and mixed forms.
- Adenosquamous carcinoma.
- Sarcomatoid carcinoma. Combines pleomorphic, spindle cell, and giant cell carcinomas, as well as carcinosarcoma and blastoma.
- Carcinoid tumors. Divided into typical and atypical carcinoids.
- Salivary gland tumors. Include mucoepidermoid, adenoid cystic, and epithelial-myoepithelial carcinomas.
Precancerous changes and early diagnostics
The classification also strictly distinguishes precancerous (preinvasive) changes in the lung tissue. These include:
- Squamous cell carcinoma in situ;
- Atypical adenomatous hyperplasia;
- Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia.
Instrumental methods are used for the early diagnosis of lung cancer. The main ones are X-ray imaging and transthoracic percutaneous lung biopsy, which provides cellular material for accurate histological analysis.
Features of peripheral lung cancer
Peripheral lung cancer is characterized by significantly greater histological diversity compared to central cancer. This is due to the specifics of its histogenesis. The tumor is associated not only with bronchial and bronchiolar cells (basal, goblet, ciliated), but also involves Clara cells and type II pneumocytes.
Among the histological types of peripheral cancer, glandular carcinomas (adenocarcinomas) are by far the most prevalent. Bronchioloalveolar carcinoma is also frequently encountered. Squamous cell and small cell carcinomas develop extremely rarely in peripheral locations.
Complications and metastatic pathways
Tumor progression leads to serious local complications. The neoplasm may invade the pleural cavity, clinically causing serous-hemorrhagic or hemorrhagic pleurisy. Tumor extension into large bronchi, as well as breakdown and suppuration of the tumor node, are also observed.
Lung cancer metastasizes via two main pathways:
- Lymphogenous pathway. Predominates in the early stages of the disease. The first metastases appear in regional lymph nodes. In late stages, bifurcation, paratracheal, mediastinal, and cervical lymph nodes are affected. Total carcinomatosis of the lungs, pleura, and peritoneum may develop.
- Hematogenous pathway. Characteristic of late stages. Tumor cells are disseminated via the bloodstream, and metastases are found in the liver, bones, adrenal glands, and brain.
Briefly: answers to topical questions
What macroscopic forms of central lung cancer are distinguished in pathological anatomy?
Pathological anatomy distinguishes four main macroscopic forms of central (hilar) lung cancer developing in large bronchi.
- Polypoid — a form of tumor resembling a polyp.
- Nodular — a form of tumor appearing as a node.
- Branched — a branched form of tumor.
- Nodular-branched — a mixed macroscopic form.
Depending on the direction of spread (growth pattern), tumors are also classified into:
- Exophytic (endobronchial) — the tumor grows into the bronchial lumen.
- Endophytic (exobronchial) — the tumor grows primarily into the bronchial wall thickness and parenchyma.
- Branched — sleeve-like peribronchial growth around the bronchi.
- Mixed — a combination of the listed components.
How is lung cancer classified according to the international TNM system?
According to the international TNM system, lung cancer is classified based on the evaluation of the primary tumor (T), regional lymph nodes (N), and distant metastases (M).
Clinical evaluation ("c") is performed before surgery, and pathohistological classification ("p") after surgery. For pN assessment, examination of at least 6 lymph nodes is mandatory, of which at least 3 must be mediastinal and 1 must be a bifurcation node.
The stage grouping includes the following:
- Occult — Tx N0 M0.
- Stage 0 — Tis N0 M0.
- Stage I — includes sub-stages IA (IA1, IA2, IA3) and IB.
- Stage II — includes sub-stages IIA and IIB.
- Stage III — includes sub-stage IIIA.
How do the macroscopic picture and growth pattern of central lung cancer differ from peripheral cancer?
The macroscopic picture and growth pattern depend on the initial localization of the tumor within the airways.
| Characteristic | Central cancer | Peripheral cancer |
|---|---|---|
| Origin of growth | Large bronchi (main, lobar, segmental) | Small bronchi, bronchioles, alveoli |
| Growth patterns | Exophytic, endophytic, branched, mixed | Nodular form, pneumonia-like cancer, Pancoast tumor |
| Macroscopic appearance | Polypoid, nodular, branched, nodular-branched | Spherical or oval shape, lobulated contours, "corona radiata" sign (corona radiata) |
To remember the five criteria for lung cancer classification, use the mnemonic: "Easy to Recognize Morphology of Complex Histology" (Localization, Growth, Macroscopic appearance, Stage, Histogenesis).
Class and exam questions
Which cells are involved in the histogenesis of peripheral cancer?
In addition to basal, goblet, and ciliated cells of bronchi and bronchioles, Clara cells and type II alveolar cells invariably participate in the tumor process.
Which histological type predominates in peripheral tumor localization?
Glandular carcinomas, particularly adenocarcinomas, are the most common. Squamous cell carcinoma and small cell lung cancer are diagnosed rarely.
How is well-differentiated squamous cell carcinoma identified on slide preparations?
The immunoperoxidase staining method is used. The presence of pancytokeratins in cancer cells serves as a diagnostic sign.
Where does lung cancer metastasize via hematogenous routes?
In late stages of the disease, hematogenous metastases are found in the liver, bones, adrenal glands, and brain.
What else to study on this topic
- Lung cancer staging according to the TNM system
- Degree of tumor cell differentiation
- Clinical and morphological characteristics and prognosis in various types of cancer
- Macroscopic appearance and pattern of tumor growth
- Molecular subtypes of lung carcinomas
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