9th January 2024

Pathophysiology

The exact mechanism by which lung cancer occurs is not completely understood. Carcinogen exposure can deactivate tumour suppressor genes (such as p53) or activate oncogenes (such as c-myc), resulting in an abnormal cell cycle. Increased exposure results in increased cell dysplasia. Smoking cessation has been shown to reduce the incidence of lung cancer, with a reduction of up to 90 percent, dependent on the time and length of cessation.

The type of lung cancer depends on which cells are involved; for example, adenocarcinoma is a cancer of glandular cells which produce mucus, whereas squamous cell carcinoma affects squamous cells which line the airways.

Lung adenocarcinomas are the commonest type of lung cancer. They are often peripherally located and are highly associated with smoking. However, amongst individuals who have never smoked, it is the commonest form of lung cancer. Squamous cell carcinomas are usually centrally located, for example close to a main bronchus. They are also closely linked to smoking. Large cell carcinomas are so-called due to the large nuclei observed under microscopy. Around 80% of lung cancers are NSCLCs.

SCLCs account for around 20% of lung cancers. These cancers are more aggressive than NSCLCs. Many patients presenting with symptoms already have metastatic spread. They have the worst prognosis of all the lung cancer subtypes.