Lung cancer classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Kim-Son H. Nguyen, M.D., M.P.A., Beth Israel Deaconess Medical Center, Harvard Medical School, Boston MA, Cafer Zorkun, M.D., Ph.D. [2]

Overview

The vast majority of lung cancers are carcinomas—malignancies that arise from epithelial cells. There are two main types of lung carcinoma, categorized by the size and appearance of the malignant cells seen by a histopathologist under a microscope: non-small cell (80.4%) and small-cell (16.8%) lung carcinoma. This classification, based on simple histological criteria, has important implications for clinical management and prognosis of the disease.

Classification

Primary lung cancer can be classified into two main categories: small cell lung cancer (SCLC) and non small cell lung cancer (NSCLC).

Lung cancer

Small cell lung cancer (~15%)

Non small cell lung cancer (~85%) Squamous cell carcinoma (25% of lung cancers) Adenocarcinoma (40% of lung cancers) Large cell carcinoma (10% of lung cancers) Adenosquamous carcinoma Carcinomas with pleomorphic, sarcomatoid, or sarcomatous elements Carcinoid tumor Carcinomas of salivary gland type Unclassified carcinoma

Small Cell Lung Cancer

• Small cell lung carcinoma (SCLC, also called "oat cell carcinoma") is less common. It tends to arise in the larger breathing tubes and grows rapidly, becoming quite large.

• The "oat" cell contains dense neurosecretory granules (vesicles containing neuroendocrine hormones) which give this an endocrine/paraneoplastic syndrome association.

• While initially more sensitive to chemotherapy, it ultimately carries a worse prognosis and is often metastatic at presentation. This type of lung cancer is strongly associated with smoking.

Non Small Cell Lung Cancer

• The non-small cell lung carcinomas are grouped together because their prognosis and management are similar. There are three main sub-types: squamous cell lung carcinoma, adenocarcinoma and large cell lung carcinoma.

• Accounting for 31.1% of lung cancers, squamous cell lung carcinoma usually starts near a central bronchus. Cavitation and necrosis within the center of the cancer is a common finding. Well-differentiated squamous cell lung cancers often grow more slowly than other cancer types.

• Adenocarcinoma accounts for 29.4% of lung cancers. It usually originates in peripheral lung tissue. Most cases of adenocarcinoma are associated with smoking. However, among people who have never smoked ("never-smokers"), adenocarcinoma is the most common form of lung cancer. A subtype of adenocarcinoma, the bronchioloalveolar carcinoma, is more common in female never-smokers, and may have different responses to treatment.

• Accounting for 10.7% of lung cancers, large cell lung carcinoma is a fast-growing form that develops near the surface of the lung. It is often poorly differentiated and tends to metastasize early.

WHO/IASLC Histologic Classification of NSCLC

• Squamous cell carcinoma
  • Papillary
  • Clear cell
  • Small cell
  • Basaloid

• Adenocarcinoma
  • Acinar
  • Papillary
  • Bronchioloalveolar carcinoma
    • Nonmucinous
    • Mucinous
    • Mixed mucinous and nonmucinous or indeterminate cell type
  • Solid adenocarcinoma with mucin
  • Adenocarcinoma with mixed subtypes
  • Variants
    • Well-differentiated fetal adenocarcinoma
    • Mucinous (colloid) adenocarcinoma
    • Mucinous cystadenocarcinoma
    • Signet ring adenocarcinoma
    • Clear cell adenocarcinoma
• Large cell carcinoma
  • Variants
    • Large cell neuroendocrine carcinoma (LCNEC)
    • Combined LCNEC
    • Basaloid carcinoma
    • Lymphoepithelioma-like carcinoma
    • Clear cell carcinoma
    • Large cell carcinoma with rhabdoid phenotype
• Adenosquamous carcinoma
• Carcinomas with pleomorphic, sarcomatoid, or sarcomatous elements
• Carcinomas with spindle and/or giant cells
  • Spindle cell carcinoma
  • Giant cell carcinoma
  • Carcinosarcoma
  • Pulmonary blastoma
• Carcinoid tumor
  • Typical carcinoid
  • Atypical carcinoid
• Carcinomas of salivary gland type
  • Mucoepidermoid carcinoma
  • Adenoid cystic carcinoma
  • Others
• Unclassified carcinoma

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Frequency of histological types of lung cancer
Histological type	Frequency (%)
Non-small cell lung carcinoma	80.4
Small cell lung carcinoma	16.8
Carcinoid	0.8
Sarcoma	0.1
Unspecified lung cancer	1.9

Metastatic Cancersa

• The lung is a common place for metastasis from tumors in other parts of the body. These cancers are identified by the site of origin, thus a breast cancer metastasis to the lung is still known as breast cancer. They often have a characteristic round appearance on chest x-ray.

References

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