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Classification and Morphology of Lung Cancer

Carcinoma pulmonum

For medical students2 min readUpdated 2026-10-10

Lung cancer classification is based on five key criteria: tumor localization, growth pattern, macroscopic appearance, disease stage, and histogenesis. The pronounced histological diversity of these neoplasms requires precise morphological evaluation for an accurate diagnosis.

CriteriaClassification is built on 5 features: localization, growth pattern, macroscopic appearance, stage, and histogenesis.

MarkersPancytokeratins are detected in squamous cell carcinoma using the immunoperoxidase method.

Peripheral cancerMost commonly represented by adenocarcinoma, characterized by high histological diversity.

MetastasisEarly lymphatic spread (to lymph nodes), late hematogenous spread (liver, bones, brain).

Histological Classification (WHO)

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. When examining a micro-slide of a well-differentiated keratinizing squamous cell carcinoma using the immunoperoxidase method, a specific diagnostic feature is revealed: the presence of pancytokeratins in the cancer cells.
Small cell carcinoma. Includes combined small cell carcinoma.
Adenocarcinoma. Includes acinar, papillary, solid adenocarcinoma with mucin production, and mixed subtypes. Bronchioloalveolar carcinoma is distinguished separately, with variants including non-mucinous, mucinous, and mixed forms.
Adenosquamous carcinoma.
Sarcomatoid carcinoma. Unites pleomorphic, spindle cell, and giant cell carcinomas, as well as carcinosarcoma and pulmonary blastoma.
Carcinoid tumors. Divided into typical and atypical carcinoids.
Salivary gland-type tumors. Include mucoepidermoid, adenoid cystic, and epithelial-myoepithelial carcinomas.

Precancerous Lesions and Early Diagnosis

The classification also strictly identifies precancerous (preinvasive) lesions of 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 primary methods are radiography and transthoracic core-needle lung biopsy, which provides cellular material for accurate histological analysis.

Features of Peripheral Lung Cancer

Peripheral lung cancer differs by having significantly greater histological diversity compared to central lung 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 alveolar cells.

Among the histological types of peripheral cancer, glandular carcinomas (adenocarcinomas) overwhelmingly predominate. Bronchioloalveolar carcinoma is also frequently encountered. Squamous cell and small cell carcinomas rarely develop at a peripheral site.

Complications and Pathways of Metastasis

Tumor progression leads to serious local complications. The neoplasm may invade the pleural cavity, clinically causing serosanguinous or hemorrhagic pleuritis. Extension of the tumor into major bronchi, along with necrosis and abscess formation within the tumor mass, is also observed.

Lung cancer metastasizes via two main pathways:

Lymphatic pathway. Predominates in the early stages of the disease. The first metastases appear in regional lymph nodes. In later stages, bifurcation, paratracheal, mediastinal, and cervical lymph nodes are affected. Total carcinomatosis of the lungs, pleura, and peritoneum may develop.
Hematogenous pathway. Characteristic of later stages. Tumor cells are disseminated via the bloodstream, and metastases are found in the liver, bones, adrenal glands, and brain.

Mnemonic

To remember the five criteria of lung cancer classification, use the mnemonic: "Lung Growth Makes Staging Hard" (Localization, Growth pattern, Macroscopic appearance, Stage, Histogenesis).

Frequently asked questions

What macroscopic forms of central lung cancer are distinguished in pathology?

Pathology identifies four main macroscopic forms of central (root) lung cancer developing in large bronchi:

Polypoid — a tumor forming a polyp in the lumen.
Nodular — a tumor forming a distinct nodule.
Branching — a tumor growing along the branching structures.
Nodular-branching — a mixed macroscopic form.

Based on the direction of spread (growth pattern), tumors are also classified into:

Exophytic (endobronchial) — tumor grows into the bronchial lumen.
Endophytic (exobronchial) — tumor grows primarily into the bronchial wall thickness and parenchyma.
Branching — sleeve-like peribronchial growth around the bronchi.
Mixed — a combination of the above 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 assessment of the primary tumor (T), regional lymph nodes (N), and distant metastases (M).

Clinical staging ("c") is performed before surgery, and pathological staging ("p") is done after surgery. For pN staging, examination of at least 6 lymph nodes is required, of which at least 3 must be mediastinal and 1 must be bifurcation (subcarinal).

Stage groupings include:

Occult — Tx N0 M0.
Stage 0 — Tis N0 M0.
Stage I — includes substages IA (IA1, IA2, IA3) and IB.
Stage II — includes substages IIA and IIB.
Stage III — includes substage IIIA.

How do the macroscopic picture and growth pattern of central lung cancer differ from peripheral lung cancer?

The macroscopic picture and growth pattern depend on the original site of the tumor within the airways.

Characteristic	Central Cancer	Peripheral Cancer
Site of origin	Large bronchi (main, lobar, segmental)	Small bronchi, bronchioles, alveoli
Growth patterns	Exophytic, endophytic, branching, mixed	Nodular form, pneumonia-like cancer, Pancoast tumor
Macroscopic view	Polypoid, nodular, branching, nodular-branching	Spherical or oval shape, lobulated contours, corona radiata sign

What cells participate in the histogenesis of peripheral cancer?

In addition to basal, goblet, and ciliated cells of the bronchi and bronchioles, Clara cells and type II alveolar cells actively participate in the tumor process.

Which histological type predominates in peripheral tumors?

Glandular carcinomas, particularly adenocarcinomas, are the most common. Squamous cell and small cell carcinomas are rarely diagnosed here.

How is well-differentiated squamous cell carcinoma identified on microscopy?

The immunoperoxidase staining method is used. The diagnostic marker is the presence of pancytokeratins in the cancer cells.

Where does lung cancer metastasize via hematogenous spread?

In advanced stages, hematogenous metastases are found in the liver, bones, adrenal glands, and brain.

Go deeper

Lung cancer staging using the TNM system
Degree of tumor cell differentiation
Clinical and morphological characteristics and prognosis in various types of cancer
Macroscopic appearance and tumor growth patterns
Molecular subtypes of lung carcinomas