Lung Cancer

Lung cancer is a malignant neoplasm arising from the cells of the lung, most commonly the epithelium of the airways. It is among the most frequently diagnosed cancers and the leading cause of cancer death worldwide, with tobacco smoking as its dominant cause.

Definition

Lung cancer is a malignant tumour originating in lung tissue, predominantly from bronchial or alveolar epithelial cells, classified principally into non-small cell and small cell types with distinct biology and behaviour.

Scope

This entry describes lung cancer as a pathological process: its major histological types, the molecular and carcinogenic mechanisms of tumour development, and its epidemiology. It is reference-educational and does not provide staging-specific, chemotherapy, targeted-therapy, dosing, or individualised treatment guidance.

Core questions

• What histological type is the tumour, and how does that shape its behaviour?
• Which carcinogenic exposures and molecular alterations drive tumour development?
• How is non-small cell distinguished from small cell lung cancer pathologically?
• How does the tumour grow, invade, and spread within and beyond the lung?

Key concepts

• Non-small cell lung cancer (adenocarcinoma, squamous cell carcinoma, large cell)
• Small cell lung carcinoma
• Tobacco carcinogenesis
• Driver mutations and oncogenic signalling (e.g. EGFR, ALK, KRAS)
• Field cancerisation of the airway epithelium
• Invasion and metastasis
• Paraneoplastic syndromes

Mechanisms

Chronic exposure to carcinogens, above all those in tobacco smoke, causes accumulating genetic and epigenetic damage in airway epithelial cells, producing a field of altered mucosa from which invasive cancer emerges. Tumours are broadly divided into non-small cell lung cancer (including adenocarcinoma, squamous cell carcinoma, and large cell carcinoma) and small cell lung carcinoma, which is strongly smoking-associated and aggressive. In a subset of non-small cell tumours, particularly adenocarcinomas, specific driver alterations in genes such as EGFR or ALK activate growth-promoting signalling, a molecular dimension reviewed by Herbst and colleagues. Tumours grow locally, invade surrounding structures, and metastasise via lymphatics and blood; some secrete hormones or peptides producing paraneoplastic syndromes.

Clinical relevance

Lung cancer is classified and staged by histology, molecular profile, and anatomical extent, and these features frame prognosis and the rationale for distinct treatment pathways. Understanding the tumour's pathology and molecular biology clarifies why histological and molecular subtyping matter. This entry is descriptive reference material and does not provide individualised treatment recommendations.

Epidemiology

Lung cancer is one of the most commonly diagnosed cancers and the leading cause of cancer mortality globally, as quantified in GLOBOCAN cancer statistics. Tobacco smoking is the predominant risk factor; additional contributors include radon, occupational carcinogens such as asbestos, and ambient air pollution.

History

The marked twentieth-century rise in lung cancer was traced to cigarette smoking through landmark epidemiological studies, including early case-control work linking smoking to carcinoma of the lung. Later decades brought refined histological classification and, more recently, the identification of actionable driver mutations that reframed the disease along molecular lines.

Debates

How central is molecular subtyping to classifying lung cancer?

Classification has expanded from histology alone toward integrated histological and molecular characterisation, especially in non-small cell lung cancer, and the relative weight of these axes in diagnosis continues to evolve.

Seminal works

• thai-2021
• herbst-2018
• bray-2024

Frequently asked questions

What is the main difference between non-small cell and small cell lung cancer?

Non-small cell lung cancer encompasses adenocarcinoma, squamous cell carcinoma, and large cell carcinoma and behaves more variably, while small cell lung carcinoma is a distinct, strongly smoking-associated, rapidly growing tumour; the distinction is fundamental to classification and prognosis.

What is the leading cause of lung cancer?

Tobacco smoking is the dominant cause; other contributors include radon, occupational carcinogens such as asbestos, and air pollution.