Lung Cancer

Definition

Lung cancer is a malignant tumor originating from the respiratory epithelium, primarily classified into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), with variable clinical behavior and prognosis.

Epidemiology

• Second most common cancer worldwide and leading cause of cancer death
• Higher incidence in smokers; also occurs in non-smokers
• Peak incidence: 60–70 years
• Slight male predominance
• Incidence varies globally with higher rates in developed countries

Etiology

• Cigarette smoking (primary risk factor, >80% of cases)
• Secondhand smoke exposure
• Occupational exposures: asbestos, radon, heavy metals, air pollution
• Genetic predisposition: EGFR, ALK, KRAS mutations
• Chronic lung disease (COPD, pulmonary fibrosis) increases risk

Pathophysiology

• Genetic mutations and epigenetic alterations lead to uncontrolled proliferation of bronchial or alveolar epithelial cells
• NSCLC subtypes: adenocarcinoma (peripheral), squamous cell carcinoma (central), large cell carcinoma (undifferentiated)
• SCLC arises from neuroendocrine cells, tends to be centrally located and aggressive
• Local invasion into bronchi, pleura, mediastinum, and chest wall
• Metastasis occurs via lymphatic and hematogenous routes (brain, liver, bone, adrenal glands)