Lung cancer

Lung cancer is a malignant tumour of the lungs. Most commonly it is bronchogenic carcinoma (about 90%). Lung cancer is the most lethal malignant tumour worldwide, causing up to 3 million deaths annually.

Types

There are two main types of lung cancer categorised by the size and appearance of the malignant cells seen by a histopathologist under a microscope: small-cell (roughly 20%) and non-small cell (80%) lung cancer. This classification although based on simple pathomorphological criteria has very important implications for clinical management and prognosis of the disease.

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Non-small cell lung cancer

The non-small cell lung cancers (NSCLC) are grouped together because their prognosis and management is roughly identical. The subtypes are:

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• Squamous cell carcinoma also starts in the larger breathing tubes but grows slower meaning that the size of these tumours varies when on diagnosis.
• Adenocarcinoma (or for slower growing forms alveolar cell cancer) is a form which starts near the gas-exchanging surface of the lung. It is less closely associated with smoking.
• Large cell carcinoma is a fast-growing form that grows near the surface of the lung.

Small cell lung cancer

Small cell carcinoma (SCLC, also called "oat cell carcinoma") is the less common form of lung cancer. It tends to start in the larger breathing tubes and grows rapidly becoming quite large. The oncogene most commonly involved is L-myc. The "oat" cell contains dense neurosecretory granules which give this an endocrine/paraneoplastic syndrome association. It is more sensitive to chemotherapy, but carries a worse prognosis and is often metastatic at presentation. This type of lung cancer is strongly associated with smoking.

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Other types

See the article carcinoid.

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The main representatives in this group are carcinoid. Rarer lung cancers include cylindroma and mucoepidermoid carcinoma.

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Metastatic

The lung is a common place for metastasis from tumors in other parts of the body.

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