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PH-RS10

Malignant epithelial lung tumours

How smoke, radon and driver mutations turn airway lining cells into carcinoma, how the main types differ in site and appearance, and how lung cancer obstructs airways, invades the mediastinum, spreads early and causes paraneoplastic syndromes.

By the end, you can

  • Relate the main causes of lung cancer to the mutations they produce, in smokers and in people who have never smoked.
  • Compare adenocarcinoma, squamous cell carcinoma and small cell carcinoma by site, microscopy and behaviour.
  • Explain how local growth produces obstruction, effusion, hoarseness, superior vena cava obstruction and Horner syndrome.
  • Describe the routes of spread and the main paraneoplastic syndromes, with their mechanisms.
  • Explain what TNM staging and grading measure, in general terms.
  • Recognise the classic microscopy, immunostains, classification, stage groups and tests of lung carcinoma, and explain how surgery, radiotherapy, chemotherapy, kinase inhibitors and checkpoint inhibitors act on it.

What it is

Lung cancer usually means primary carcinoma of the lung, a malignant tumour of the epithelial cells lining the airways and alveoli. The main types are adenocarcinoma, squamous cell carcinoma and the neuroendocrine carcinomas (small cell and large cell neuroendocrine carcinoma), with carcinoid tumours as low- and intermediate-grade neuroendocrine tumours. Clinically, carcinomas other than small cell carcinoma are often grouped as non-small cell lung carcinoma.

4 types to tell apart
Adenocarcinoma
The commonest type, including in never-smokers; usually peripheral; forms glands, papillae or mucin.
Squamous cell carcinoma
Strongly linked to smoking; usually central, from squamous dysplasia; makes keratin.
Small cell carcinoma
High-grade neuroendocrine carcinoma; central, fast-growing and usually spread at diagnosis; strongly linked to smoking.
Carcinoid tumours
Typical (low grade) and atypical (intermediate grade) neuroendocrine tumours, often central and polypoid; not related to smoking in most cases.

US spelling: tumours → tumors, tumour → tumor, centre → center.

Normal function

The airways, their lymph nodes and the route to the blood

Air reaches the alveoli through the , the and their lobar and segmental branches. The bronchi are lined by ciliated epithelium with basal, goblet and neuroendocrine cells; the periphery by club cells and type I and II pneumocytes. Almost all primary lung cancers arise from these lining cells, so almost all are carcinomas.

Lymph from the lung drains towards the centre: to nodes within the lung and at the hilum, then to the round the , the and on to the supraclavicular nodes above the collarbone. Blood leaves through the pulmonary veins to the left heart, which pumps it to the whole body.

The lung is also one of the commonest sites of metastases from cancers elsewhere, because blood from every systemic vein passes through its capillaries. A nodule in the lung is therefore not always a primary lung cancer.

Point to it on the model